Metroid

''For the page on the Metroid Prime sub-series, click here. For Metroid: Other M, click here.''

"Must restore peace! Must escape! Peace of the universe is once again restored. HOLY CRAP I'M A GIRL!!!!!!"

- Brental Floss: "Metroid" in 5 seconds

Metroid is the story of Bounty Hunter Samus Aran, who, armed with modular cybernetic Powered Armor from an ancient civilization, repeatedly crosses paths with a species of energy-absorbing animals known as "Metroids," usually foiling the attempts of a band of Space Pirates to exploit the creatures as a weapon.

The Metroid franchise is somewhat unusual among platformers, especially Nintendo produced ones, for the substantial continuity which exists between the games. The first (NES) game was released in 1986 and deals with Samus's assault on the Space Pirate base on Zebes. After defeating the Mother Brain, Samus is dispatched in the (Game Boy) sequel, The Return of Samus (1991), to hunt down evolved Metroids on their home world. The end of this game segues directly into (Super Nintendo) Super Metroid (1994), where the final larval Metroid is stolen by space pirates who return it to a rebuilt base on Zebes.

The series lay dormant for years, skipping the Nintendo 64 entirely. The last 2D game, and the "latest" title in the continuity, Metroid Fusion (Game Boy Advance) was finally released in 2002, wherein the Metroid homeworld has been overrun by a shape-shifting parasite which the Metroids kept in check. The series took a turn towards Survival Horror with this game; both a lab orbiting the Metroid homeworld and Samus herself fall to the new threat, so a severely-weakened Samus is infused with Metroid DNA to save her life and sent in to investigate. A sequel, tentatively titled Dread, has been stuck in Development Hell for the past ten years, and is intended to follow on from the end of Fusion.

At the same time, Nintendo had made the controversial decision to move the series into 3D on the GameCube, with an American studio known as Retro Studios at the helm. The gamble paid off, and Metroid Prime emerged as an unusual FPS-adventure, set between the first and second games, which met with great critical acclaim. In addition, Retro Studios ended up being purchased by Nintendo, making it Nintendo's second American first-party developer after Nintendo Software Technology Corporation.

The first game was remade for the Game Boy Advance a year later as Zero Mission. The 3D installments have become a franchise in their own right, with Metroid Prime 2: Echoes (GameCube), and Metroid Prime Hunters (Nintendo DS) continuing the in-between storyline, which was finally finished in 2007 with Metroid Prime 3: Corruption (Wii), completing the Phazon Arc. Tropes belonging exclusively to this sub-series belong here.

The latest game, Other M (Wii), was released at the end of August 2010, and combines elements from both series. It was worked on by the unusual combination of the inhouse team responsible for the Metroid series and none other than Team Ninja. Whether or not the developer and gameplay shifts were a success or not depends greatly on who you ask. Trailer can be seen here. It takes place between Super Metroid and Metroid Fusion, making it the only game since Fusion to take place after Super.

Across the entire franchise, a number of characteristic elements have persisted, such as the continuous string of upgrades which Samus acquires over the course of the game (The Metroid Prime games open with a scene in which Samus has the advanced weapons of the previous game, then loses them. This also happens during the opening narration to Metroid Fusion), most notably the "Morph Ball" (or "Maru Mari," one of several translation oddities), which allows Samus to contort into the shape of a small ball, for better maneuverability in areas where this shape is more convenient.

This series is also known for being one of the two best known series of Metroidvania games, as implied by the name. (These are action adventure games with an emphasis on exploring a continuous and non-linear play world and finding powerups to advance.)

Technologically, the original Metroid is noteworthy as one of the first multi-way scrolling platformers. Its North American release was also the first game to use a password system to save progress. The original Japanese release of Metroid was for Nintendo's disc-based system, and allowed the players to save their progress on the disc. Since the cartridge-based US system lacked this ability, the player was presented with a 24-character password which encoded the state of the game, allowing the player to resume his or her progress later.

The ending of the original Metroid is also a Tomato Surprise: if the player did sufficiently well during the game, he is treated to a (then) stunning revelation: Samus Aran's armor is removed, revealing the bounty hunter as a shapely (by 8-bit standards) woman. This reveal is also in most of the other games -- although no longer a surprise -- at or near the ending. Those who Read the Freaking Manual would find that Samus is openly referred to as a female by Metroid 2.

Though Samus herself has never appeared on television (except in commercials), Mother Brain was featured as the Big Bad of the Nintendo-themed animated series Captain N: The Game Master. (Reportedly, the production staff actually didn't know about Samus); the comic book adaptation introduced her as the Sixth Ranger / The Lancer.

A live-action feature film based on the franchise was optioned after Metroid Prime was successful, but appears to have lapsed.


 * Metroidvania along with the Castlevania series, obviously.
 * Samus Is a Girl again, obviously.

A-F

 * Abnormal Ammo: Samus has been shot at with explosive stingers, lava grenades, super cooled plasma, high density neutrinos, and contaminated water.
 * Samus herself has fired plasma, super-cooled plasma, ice, lava grenades, electromagnetic blasts, standard electrical blasts, concentrated light energy, concentrated dark energy, matter/antimatter, sonic booms, miniature black holes, and various other things out of her own beam cannon. And that doesn't account for projectile weapons - missiles, super missiles, ice missiles...
 * Action Girl: One of the earliest video game examples, and easily one of the most well-known.
 * Aerith and Bob: Several enemies have weird names like "Desgeega" or "Holtz", or portmanteau names like "Crocomire" and "Sidehopper". A seahorse-like enemy in Norfair that spits fire at you? "Dragon".
 * Speaking of dragons, one must not forget Ridley, the giant Space Dragon/Pirate Commander, who's an example of this trope as he has the completely normal human name of Ridley despite being a Dragon Space Pirate Alien. What are the other alien's names? Kraid, Phantoon...
 * Among the humans we have Adam, James, Lyle, Ian, K.G. (Keiji), Anthony... and Samus.
 * After Boss Recovery: Many bosses and mini bosses drop tons of health and ammo refills when you beat them.
 * Justified in Fusion as all the bosses and enemies are made of X parasites that Samus absorbs to recover health, so it makes sense that the bigger bosses have more potent X for her to eat.
 * Air Vent Passageway: Applies to all kinds of ducts/tunnels, with the Morph Ball. Subverted in Zero Mission, when after, Samus must crawl through said tunnels, and she's far from the only creature who can use them.
 * All There in the Manual: The games are easy to understand plotwise on their own, but there's quite a bit of canonical backstory for both Zero Mission and Fusion, as well as the entire franchise on the whole, to be found in the manuals and the two-volume manga.
 * Always Lawful Evil: The Space Pirates. Justified, as it's claimed any space pirates who question The Way Things Are are executed, sometimes on the spot. Any space pirate who expressed non-evil thoughts wouldn't have a very long life expectancy.
 * According to some scans in the Prime series and some out-of-game info, not all of them are very happy with evil being the law, and certain POWs were incredibly easy to interrogate. Other scans seem to paint them more as Lawful Stupid, with common troops not being nearly as malicious or cunning as Science Team.
 * Ambidextrous Sprite: Averted in all 2-D games after the first; Samus has different sprites for all directions. In fact, this may only be played straight by the NES version; in commercials for the Famicom game, she has unique sprites for facing left and right.
 * Androcles' Lion: A major plot element in the series. In Metroid II, Samus is tasked with exterminating the Metroid species, but stops at killing a newborn. In Super Metroid, the baby is kidnapped, and Samus goes to get it back. This episode is the major thematic introduction for Metroid: Other M.
 * In Super Metroid, Samus saves some Etecoons and Dachora during the escape sequence. At the escape sequence in Fusion, the same animals help control the gunship to escape the space station.
 * It also occurs in in Metroid: Fusion, in a posthumous example. After Samus is infected by the X parasite, a cell sample of the same baby Metroid is used as part of the cure that destroys the parasites inside her and saves her life.
 * Anticlimax Boss: Arguably, the in Fusion; not only is it nowhere near the strongest boss in the game, it isn't even as strong as its previous appearances in Metroid II. However, it's arguable whether it counts as the final boss; most fans believe that the SA-X is the true final boss, and.
 * Kraid in Super could be taken out with two well-timed super missiles before he even finished rising up from the ground. Ostensibly a glitch, Kraid can be defeated in little time even without it by a seasoned player.
 * And Mecha-Ridley in Zero Mission, who is incredibly easy. He gets more challenging, however, if you've gotten 100% of the items, or if you're doing a 15% item run.
 * Arm Cannon: Might even qualify as a Hand Cannon.
 * Artificial Stupidity: Despite the fact that the SA-X is the most powerful enemy in all of Fusion, and despite the X's ability to copy any organic body part, it apparently lacks a brain.
 * Apocalyptic Log: The ROM Hack Super Metroid Eris.
 * As You Wish: How Samus discovers the identity of her AI CO in Metroid Fusion.
 * Many fans realized what the mysterious trailer for Other M was as soon as Adam said "Any objections, lady?" Prior to this, it was intentionally unclear what the game in question was.
 * Asteroid Thicket: Used in Super and Fusion, where something crashes into an asteroid in each. The asteroids look like they're only a few hundred feet across, and tightly packed.
 * Attack of the 50-Foot Whatever: Kraid in Super Metroid and Zero Mission, Metroid Prime, the Adult Sheegoth, Flaaghra, Thardus, Chykka, Quadraxis, Mogenar...
 * Back Tracking: Obtain previously inaccessible power-ups, curb-stomp previously lethal opponents with your new upgrades, and discover brand new shortcuts and secrets -- all by the magic of backtracking through every area of the game at least twice.
 * It is so integral to this series that fans will frequently complain if the developers remove the ability to backtrack, such as in Metroid Fusion and Metroid: Other M. Even those at least give full access to the game world once Samus is fully upgraded.
 * Badass: Samus. So very, very much.
 * Bag of Spilling: Samus never manages to keep her fully powered-up suit between games, though more recent entries at least let her hang onto the Varia upgrade. Usually.
 * Played with in Metroid Fusion. Samus kept all of the weapon upgrades to her power armor. Unfortunately, her power armor was infected with a parasite which is now using all of those weapon upgrades to try to kill her.
 * And in Prime. While trying to escape the ship at the beginning of the game before self destruction, the ship violently rocks to the side, and a small explosion hits her from behind, causing her to slam against the wall, which causes malfunctions with most of her equipment.
 * And again in Other M. Samus has her full arsenal, but is working with the military in this one and needs authorization to use parts of it.
 * Beauty Is Never Tarnished:
 * In Fusion, Samus has to have her suit surgically removed, and there is absolutely no scarring. There also appears to be no visible changes caused by the infusion of Metroid DNA (or Chozo DNA, for that matter).
 * Averted in Corruption. Samus's phazon corruption causes visible breakdowns on her face, and she vomits a couple times.
 * Beauty Mark: Samus, natch. Previously hinted at by Yoshio Sakamoto who claimed to be the only one who knew where it was. Its location is finally shown in ''Other M": under the left side of her lip.
 * Bee People: The Space Pirates in the manga comics will follow anyone with enough strength or charisma. In a bit of a subversion, their species can't produce "queens", so they look to other species to lead them. On their own, they're Too Dumb to Live.
 * Berserk Button: If Samus is pointing her arm cannon at you and you just happen to be a member of a race of intergalactic bloodthirsty aliens, don't beg for mercy.
 * What's that? You just killed someone Samus cares for? We'll miss you. She won't.
 * Big Bad: Mother Brain in Metroid and Super Metroid.
 * Big Boo's Haunt: The Chozo Ruins (Prime) and the Wrecked Ship (Super).
 * Big Damn Heroes: Two times, one in Super Metroid and another in Fusion. In Super,
 * And then in Fusion,
 * Bittersweet Ending: Almost every game since Super has one. The exceptions are Zero Mission and Hunters.
 * Hunters barely even had a story, and it was far from making any sense.
 * Body Horror: The X Parasites in the main series; Phazon in Prime. Metroids themselves might count, given their habit of turning their victims into desiccated gray husks that turn to powder when touched. In Prime as well, a vague reference to Space Pirate attempts to replicate the Morph Ball that went horribly, horribly wrong.
 * Special mention goes to Prime 3, where you can actually see the effects of Phazon corruption on Samus. Those eyes could curdle milk.
 * Book Ends: Super Metroid opens and closes with escapes from structures that are about to blow up.
 * In a way, both Metroid and Super Metroid (and possibly even Fusion) qualify. Metroid and Super Metroid both take place on Planet Zebes. Samus ventures into the planet once, defeats Ridley, Kraid, and Mother Brain, and escapes before the planet blows up. In Super Metroid, the end to the original trilogy, Samus ventures into the planet again, kills Ridley, Kraid, Phantoon, Draygon, and Mother Brain, and escapes before the planet blows up. Fusion, however, provides two different kinds of book ends. The end to the original trilogy had And there's also the ending, in which the SA-X, which you have been both chasing and running away from since the beginning of the game,
 * Boss Arena Recovery
 * Boss Dissonance: Zero Mission has Mario-type bad on Normal. The final boss gets significantly more challenging if, but by that point, you're so armed to the teeth anyways, it barely matters.
 * Going for a <= 15% run on hard, on the other hand, turns the above on its head and into a harsh Kirby-type.
 * Brain In a Jar: Mother Brain, the Aurora Units, and the B.O.X. security robot.
 * Brain Uploading: in Metroid Fusion.
 * Breath Weapon: Ridley, as he's a Space Dragon. Also Kraid and . In the Prime series, Sheegoths, the Parasite Queen, and.
 * Broken Bridge: Sometimes intentional, to at least try to prevent Sequence Breaking.
 * Building Swing: Grapple Beam.
 * Canon Foreigner: Captain Nemo in the old Metroid Manga/Strategy Guide, and moveset wise, the Zero Laser from Super Smash Bros.. Brawl and the "Chozo Blood Rights" ability from Marvel Ultimate Alliance (she was Dummied Out from the latter game, however).
 * Canon Immigrant: Old Bird, one of Samus's Chozo mentors/adoptive parents, appears in the Japanese version only endings of Metroid Fusion (which you can thankfully unlock in any version of Zero Mission), and makes a blink-and-you'll-miss-it cameo appearance in Metroid Zero Mission in one of Samus's flashbacks. Old Bird first appeared in the Nintendo Power Super Metroid comic and was later imported to the manga (along with Chairman Keaton and Chief Hardy). Some speculate that the second Chozo in the engraving at the end of the game may be the other Chozo mentor, Gray Voice.
 * While the character was first named and given a backstory in Fusion, Adam Malkovich's actual appearance wasn't revealed until the manga. This design is then used in Other M.
 * Catastrophic Countdown
 * Super Metroid plays it straight, twice. When Ridley escapes the space colony in the beginning, an announcement claims that the colony's self-destruct has been activated, urging immediate evacuation. Naturally, the whole place starts shaking, steaming, blowing up, and even rocking back and forth quite impressively. Later at the end of the game, the entire planet starts exploding and flooding with acid, because a "Time Bomb has been activated".
 * Other M. An AI voice announces over an intercom that a self-destruct sequence will detonate in about five or so minutes. For some reason, your escape becomes riddled with burning debris and wreckage.
 * The first game is a bit of an interesting case. While the NES original averts it entirely ("TIME BOMB SET GET OUT FAST!", plus a countdown, that's it), Zero Mission retcons in a straight example (the "time bomb" causes explosions and flames well before going off) and an aversion (the Pirate Mothership).
 * Chain-Reaction Destruction: Many bosses and planetary bodies exhibit that behavior.
 * Charged Attack: Charge Beam, Shinespark.
 * Charge Meter
 * Chekhov's Gunman:
 * Chekhov's Skill: Every power-up becomes useful to go to unreachable areas/items.
 * Classic Cheat Code By Accident: The famous ' code is just a side-effect of the password calculation system and is but one of many codes that bestow Samus with a leotard. The far less famous ' (Not A Real or North American Release Password) actually is a special, unique password, however.
 * Sadly, the above code has now become a system-killer in the 3DS port.
 * Clipped-Wing Angel: SA-X.
 * Colony Drop: BSL, at the end of Fusion.
 * Colossus Climb: Kraid, although you jump on improvised platforms instead of climbing.
 * Color Coded for Your Convenience: Doors except Return because of monochrome, in which case they're Missile doors.
 * Comic Book Adaptation: There are tons of them. Two of which are tongue-in-cheek semi-guide books, one is a Nintendo Power comic, one is loosely based upon the first Metroid Prime, a prequel manga and a manga based on pre-MP2. Let's not even get started with Samus and Joey series...
 * Continuity Nod: The remixed music in the latest installments, plus pieces of the original Brinstar and Tourian in Super Metroid. Possibly also parts of Kraid and Ridley's lairs, although Kraid's "Lair" (especially the piece in question) is very far from where it ought to be.
 * Something of a Call Forward: The temple that you must sneak through at the end of Metroid Zero Mission? It's part of Maridia from Super Metroid, before presumably sinking into the lake. The Pirate Mothership, however, while in the same spot as Super Metroid's Wrecked Ship, is a completely different craft.
 * Convection, Schmonvection: Averted, in a rare video game example. Without her Varia Suit, Samus can't even get near lava without being burned, and walking into superheated rooms will cause her to take continuous, non-trivial damage. Most Metroid games make the lava dangerous to touch even when the Varia Suit provides resistance to convection; only more powerful armors like the Gravity Suit allow her to walk in lava without getting hurt. In Fusion, she gains a vulnerability to extreme cold as well, as a side-effect of the Metroids DNA she was injected with.
 * And in Other M, her commander sends Samus into a lava area without letting her use the Varia upgrade. Fans did not take that well.
 * It should be noted that the only two games to play Convection, Schmonvection straight are the original Metroid (hey, it was 1986...) and Metroid II: Return of Samus, in which most players couldn't even tell it *was* lava until they explored a section of Metroid Fusion built to simulate the game... ...or saw a picture in Metroid II's manual.
 * Cool Starship: Samus' gunship, natch. The loaner ship she gets from the Federation after totaling her own in Fusion's opening may count as well.
 * Copy and Paste Environments: One of the reasons that the original is hard as hell, especially for people who played the sequels; this was, however, crucial in making a fairly large world without running out of cart space.
 * The upshot is that many of the secret area entrances are copy-and-pasted as well, so finding one can make it easier to find others in the same area.
 * Cowboy Cop: In the manga, Samus herself, as well as her partners Mauk and Kreatz.
 * Critical Annoyance: Dua-dua-dua-dua-dua-dua -- few things are better motivation to search for energy.
 * Crosshair Aware: Space Pirates have an annoying tendency to twitch themselves just out of your firing path during the Unexpected Gameplay Change stealth sequence in Zero Mission.
 * Cute Bruiser: Samus' pet, Pyonchi, is a rabbit-squirrel from her home planet, who has been known to beat the crap out of schoolyard bullies, complete with a sign saying "Play nice."
 * Roundness Proximity: Samus had this often in one of the gag mangas.
 * Cybernetics Eat Your Soul: For the most part averted, as most characters get along just fine with their cybernetically-enhanced Powered Armor.
 * Ghor is a special case. Though he's only 6% organic, he's a very nice guy. When he interfaces with computers or his battle armor, though, he becomes aggressive and bloodthirsty.
 * Damn You, Muscle Memory!: Most gamers familiar with platformers go from left to right out of habit, but the original Metroid forces you to go left in the first area to get the Morph Ball and continue... which is Fridge Brilliance, as Metroid was one of the first games featuring a sprawling open ended world. Making players go left was a way to make players realize that this wasn't just some sort of sci-fi Mario/Pitfall/Whatever game.
 * Perhaps in homage to this, the path to the right is blocked off entirely at the start of Super Metroid (until you get the speed booster and/or power bombs) and for the entirety of Fusion, as the only path out of the docking bay is to the left.
 * Darker and Edgier: While Metroid itself is already kind of the Darker and Edgier alternative to Nintendo's other franchises, the earliest version of Metroid Fusion (then just called "Metroid IV") was... very unusual. It sported a "bladed" logo, a number that looked like it was torn from a claw, a darker color scheme, and a new suit that made Samus look hyper-muscled.
 * Death Is Cheap: Ridley has died six times in the course of eight games, and twice more outside of canon. He's probably going to die again in Other M. And yet, he keeps coming back EVERY. FREAKING. TIME.
 * In Other M, she almost lampshades this when she's extremely distressed that no matter how many times she puts him down, he just keeps coming back. Considering he killed her parents, she is entitled to be a little upset.
 * More specifically, Ridley was destroyed in the first Metroid, then rebuilt as Meta-Ridley to be blasted in Metroid Prime, then rebuilt again in Corruption,, and then finally destroyed for good in Super Metroid. Then was frozen, then . Ridley very well may be gone for good, but he's the most recurring boss in the entire series, the most recurring character outside of Samus herself, and the most emotionally jarring. He even appears as a boss in Super Smash Bros..
 * Defeat Equals Explosion: Most bosses in the series will explode. This is somewhat problematic for recurring bosses such as Ridley, who has managed to come back from complete annihilation several times throughout the series.
 * Depth Perplexion: Justified. Samus can shoot through walls, but only if she has the Wave Beam, which explicitly has the ability to penetrate solid matter.
 * Determinator: Nothing will stop Samus Aran.
 * And nothing will stop Ridley from trying to take her down. Not even his own "deaths."
 * The Space Pirates, although they get their space-faring asses handed to them all too often, never give up their goal of galactic domination. Their penchant for finding Phlebotinum and Sealed Evil in a Can lying around might support this.
 * Destructible Projectiles: In various games of the series (Super Metroid in particular), certain projectiles can be destroyed for health or Missile refills during boss battles.
 * Destructive Savior: It seems Samus cannot escape the cold hand of destruction, whether it be a large base or the entire planet. So far, her "kill count" includes Dark Aether, Phaaze, Zebes, and SR388, the third of which wasn't even her fault. Granted, the others were of her own doing, Phaaze because it kept popping out Phazon Leviathans to infect other planets, Dark Aether because it was just evil, and SR388 so she could wipe out the X Parasites, but still. Not even space stations are safe, since the Biologic Space Labs orbital station dies with SR388. And Samus' first order of business on Tallon IV? Blow up the Space Frigate.
 * Heartwarmingly averted with Tallon IV and Aether. You can scan the planets via satellite in Prime 3, and learn that both are recovering from the events of the first two games. The Luminoth are rebuilding their civilization and Tallon IV's native life is thriving again.
 * Doom Magnet: In addition, very few characters with personal connections to Samus ever survive. Ridley doesn't count.
 * Guess what happens to the Bottle Ship at the end of the Playable Epilogue of Metroid: Other M? The music is even the same as during the escape sequence in Super Metroid.
 * And no mention goes to the Ceres Space Colony? It wasn't her fault, but it still did collide with an asteroid and blow up right when she left it. And then there's Samus' own ship in the Fusion prologue, but again, not her fault. She lost consciousness and the ship also collided with an asteroid.
 * Diabolus Ex Machina: The extended story of Zero Mission is kicked off by
 * Die Hard On An Entire Planet: Except when it is on a space station, complete with air vent escapes and everything!
 * Disney Death: in Metroid: Other M with some clever enemy manipulation.
 * Doomed by Canon: See Foregone Conclusion.
 * Doomed Hometown: Samus lives through two of these, first on K-2L and then on Zebes.
 * Doppelganger Spin
 * Do Well, But Not Perfect:.
 * Down the Drain: Maridia, the crashed frigate, Torvus, Sector 4 - AQA.
 * The Dragon: Ridley is a high-ranking member of the Space Pirates under Mother Brain, and is typically the second-to-last boss fought in every game. He also takes the trope to its literal extreme.
 * Dumb Muscle: The original Japanese strategy guide was also a manga; Samus was depicted as a trigger-happy ditz with far more strength than smarts.
 * Dummied Out: Two very interesting things were removed at some point from Zero Mission. One was the ability to turn suit upgrades on and off from the pause menu, as in Super Metroid; fans are still wondering why this much-missed feature was taken out. (Cheat codes can turn it back on.) The second was... Crocomire! This Super Metroid boss was found in the ROM, with a full set of sprites and some movement code, but nothing else. It's possible to hack him into various rooms.
 * In turn, Super Metroid's ROM includes some interesting objects that were never used, most notably a "reflector" which would bounce any beam or missile off at a 90-degree angle. A form of this was used by two pirates in Ridley's Lair who act as a miniboss.
 * Dungeon Bypass: The Shinespark.
 * Early Installment Weirdness: By the truckload. The 1986 design for Samus Aran gave "his" suit a large red barrel chest, tubes under both arms, a more "ray gun" barrel on the cannon, a red glove, and red boots. In addition, the artwork for enemies in the NES version of the game differed considerably from the Famicom version. In both, Kraid was a stout, yellow lizard with long green hair. Ridley, however, resembled a cute baby dragon in the Famicom art, and a bizarre horse-mouthed creature with five eyes (three down the forehead) in the NES art.)
 * And that's just for artwork. The gameplay lacks many of the refinements found in the latter ones (maps, shooting kneeled/diagonally), and put it straight into Nintendo Hard territory.
 * As for Samus' trademark Varia Suit upgrade, in the original Metroid it's simply a color swap of her original suit. The Varia Suit didn't gain its trademark shoulder pads until Metroid II, where the change in costume had to be conveyed with a proper sprite change because of the Game Boy's graphical limitations.
 * Earthshattering Kaboom: Lots. See also: Zebes at the end of Super Metroid, Dark Aether at the end of Echoes, Phaaze at the end of Corruption, and SR388 at the end of Metroid Fusion.
 * Elaborate Underground Base: Arguably, every game features at least one (or ARE one), though Tourian (both versions) is probably the most classic example.
 * Eldritch Abomination: Phaaze is a living, sentinet planet intent on infecting as much of the galaxy as possible with Phazon, Gorea is a starborn monster capable of assimilating anything and everything thrown at it, and Phantoon is a bizarre alien parasite ghost that can fuck with local space-time and looks a fair bit like something out of the Lovecraft playbook.
 * Eleventh-Hour Superpower: Beginning with Super, most Final Bosses have a weapon used only against them.
 * Emergency Weapon: The stun pistol in Zero Mission.
 * Episode Zero the Beginning: Zero Mission
 * Eternal Engine: Tourian, and most of Fusion.
 * Even Evil Has Standards: Subverted in the manga. Ridley at first seems to avoid trying to kill Samus, but was instead lowering her guard. She's 3 years old at the time.
 * Everything's Better with Spinning: Screw Attack.
 * Evil Is Visceral: Mother Brain and the Aurora Units are big brains in jars that do not look very pretty. Starting from the first game, the Metroids themselves have visible blood vessels of some sort. In the second game, they were given an insectoid life cycle. In the third game, one of them grows really big, letting you see even more organic bits inside of the body.
 * Same goes for Dark Samus in the Prime series: the more beat-up she gets, the more glowy Phazon innards start showing. And then the same thing starts happening to Samus herself in Corruption. Let's just say it isn't pretty.
 * Evil Twin: SA-X.
 * And Dark Samus in Prime 2 and Prime 3.
 * Exactly What It Says on the Tin: "Choujin-zoku" roughly translates to "bird race". The Chozo are, y'know...
 * There's actually more. "Choujin" is "bird people," which is roughly what the Chozo are. However, "choujin" for "bird people" is phonetically the same as "choujin" for "superhuman."
 * The Metroids as well. "Metroid" is revealed to be Chozodian for "ultimate warrior". In the early games, Metroids were near-invincible, and by far the most dangerous non-boss enemies around.
 * And the Space Pirates are... Well, pirates. In Space.
 * Excessive Steam Syndrome: In the intro level for Super Metroid, Samus needs to escape a space station, while avoiding gushes of steam coming out from practically everywhere. Getting hit by the steam doesn't cost you energy, but you lose precious time to escape.
 * Expanded Universe: Many characters and stories such as Chairman Keaton, Chief Hardy, Old Bird, Adam Malkovich, and Armstrong Houston made their first appearances and/or are fleshed out in the Japanese manga and the Nintendo Power Super Metroid comic.
 * Exposition Fairy: Adam in Fusion.
 * Face Ship: Samus Aran's Gunship has the design of her helmet built on it.
 * Fake Skill: And not just in Sequence Breaking form either. Glitching Kraid in Super Metroid for instance, is not a sequence break, but certainly counts.
 * Fan Service: Your reward for finishing the game with 100% completion in most games.
 * Also, Samus' death scenes in Super Metroid, Metroid Fusion, and Zero Mission in particular show her armor blowing off, leaving her in a skimpy outfit before the screen fades to white.
 * The Federation -- The Galactic Federation.
 * Fly At the Camera Ending: In Super Metroid and Zero Mission.
 * Force Field Door: A staple of the games. Doors that open simply by being shot are handwaved as being set up to keep out unwanted wildlife. Certain fluff scans suggest they don't always succeed.
 * Foreboding Architecture
 * Foregone Conclusion: Judging from the dialogue in Fusion, Adam Malkovich will in Other M.
 * Other M also explains why
 * For Massive Damage: The traditional way to kill Metroids has been to freeze them with the Ice Beam and then shatter them with a rocket.
 * Freeze-Frame Bonus: Two in Super Metroid.
 * The more well-known one involves a small blip flying away from Zebes's ruins at the end of the game, indicating that some creatures you rescued have safely made it off the planet.
 * The other is far less significant but still awesome nonetheless: During your escape from Ceres at the beginning of the game, one of the doors will actually explode behind you, leaving behind an impassible hunk of glowing hot metal. This one is a lot more likely to go unnoticed, due to all the other explosions and random chaos on screen (not to mention that your escape is timed.) It's also the only instance of a door exploding in the entire game.
 * Freeze Ray: A vital tool of the series, both for its creative uses, and for stopping the titular threat.
 * From a Single Cell: X-Parasites, if not absorbed, will simply reform into another body.
 * Also from Fusion, the Federation had preserved a Metroid cell culture from the Metroid Hatchling. A vaccine made from these Metroid cells was used to cure Samus when she was infected by an X in the game's intro.
 * Fungus Humongous: found in a few corridors of Crateria in Super Metroid, yet noticeably absent in Brinstar. Also, the Phazon-irradiated mushrooms in the Phazon Mines.
 * Mushrooms also appear near the entrance to Tourian in Metroid: Zero Mission, which is in a section of Brinstar close to Super's "green" zone, but otherwise still rocky.
 * Fungus Humongous: found in a few corridors of Crateria in Super Metroid, yet noticeably absent in Brinstar. Also, the Phazon-irradiated mushrooms in the Phazon Mines.
 * Mushrooms also appear near the entrance to Tourian in Metroid: Zero Mission, which is in a section of Brinstar close to Super's "green" zone, but otherwise still rocky.

G-L

 * Game Mod: Super Metroid has several. Of the complete overhauls of the game, amongst the best are probably Super Metroid Redesign, Golden Dawn, Super Metroid Dependence, Super Metroid Limit, and Metroid Legacy. Other good ones include One Room, T-Metroid, Magma, and Reverse. Of these hacks, Metroid Legacy is by far the easiest, being only negligibly more difficult than the original game (there are a couple of segments that require the use of "glitches" like the mockball and the wall jump, but by and large there is very little trickery required to complete it). Golden Dawn is somewhat more difficult, but still not that difficult. Most of the others are at the very least Nintendo Hard and often descend gleefully into Platform Hell territory. Redesign, for example, has a segment where you are required to go into the toxic regions of Norfair without the Varia Suit, and must progress rapidly and kill enemies in order to survive. (There is a way to get the Varia Suit before this with Sequence Breaking, but the sequence break is probably even more difficult). Worth special mention is Super Metroid Impossible, a "slight" overhaul of the original game that, thanks to the withholding of crucial items and strategic placement of obstacles, brings it up to Kaizo Mario World levels of difficulty. It is also worth noting that, while most of these hacks are roughly equal in size to the original game, Redesign is absolutely gigantic, being maybe three times the size of the original game. Redesign is also unique among Super Metroid hacks for significantly altering the original game's physics, which makes playing it a significantly different experience from playing any other Metroid game.
 * Genius Bruiser: Samus herself; in addition to being twenty different flavors of Badass, she is also apparently quite learned in biology and electronics, and she designed her own gunship. She also shows a fairly philosophical leaning in the few internal monologues and journal entries we hear.
 * Ridley is also supposedly very intelligent, in addition to being a super-powerful space monster. It's All There in the Manual.
 * Ghost Ship: Literally, with the Wrecked Ship from Super, with the ghost-boss Phantoon, the GFS Valhalla from Prime 3, and the Bottle Ship from Other M to a lesser extent.
 * Go for the Eye: Frequently.
 * Grappling Hook Pistol: Grapple Beam.
 * Gratuitous Japanese: Maru Mari means something akin to "rolling into a ball". It's the only item in the original Metroid to keep its Japanese name in some translated releases.
 * Guide Dang It: 100% Completion is HARD.
 * Prime 3 is the only game in the series to really cut you a break on this. At a certain point in the game, you can launch exploration probes to the various planets you visit. These probes will report back every collectible you have yet to pick up. There are still a handful of items that reside on a derelict ship that you absolutely need to find yourself but otherwise, it is within reason for everyone who plays the game to get 100% without consulting a third party source.
 * Hailfire Peaks: Practically every zone in Fusion is "X meets Eternal Engine". The original and Super had a lot of "Underground Level meets X".
 * Half-Human Hybrid: Samus is a genetically augmented human with Chozo DNA, and then later receives an anti-X "vaccine" made from Metroid cells, which allows her to eat the X as if she were a metroid.
 * Happily Adopted: Samus considers the Chozo her "real" family as much as anything, and they certainly don't skimp on their love for her.
 * Fans who'd grown to associate Samus with this trope were understandably peeved when in Other M Samus refers to Adam as "the only father figure she'd ever known".
 * Has Two Mommies: In the manga, Samus' two primary caretakers are Old Bird and Gray Voice, two presumably male Chozo elders. However, in the games, her younger self's depiction of her "parents" includes a third Chozo never shown in the manga. This may be Platinum Chest.
 * He Who Fights Monsters:
 * Heartbeat Soundtrack: In Metroid Fusion, heard when the SA-X is near, but when not in "Chasing you down and trying to kill you violently"-mode. This is basically its Leitmotif.
 * Heart Container: Energy Tanks.
 * Heroic BSOD: Happens in the manga.
 * Happens as well in Metroid: Other M, and it's a huge source of controversy among Metroid fans.
 * Heroic Mime: In Prime 3, the first voice-acted game in the series, she has no voice acting beyond her usual grunts, on the grounds that Samus talking would be "too creepy." In Fusion, she's a veritable chatterbox, but it's mostly internal monologue.
 * Now she'll be talking in Other M, which, combined with the fact that she had verbal taunts in Brawl, seems to suggest she's going the "talking hero" route.
 * Heroic Sacrifice: Samus almost attempts one in Fusion
 * In Other M,.
 * And, of course,.
 * He Was Right There All Along: Acid Worm, Ridley in Zero Mission, Torizo...
 * Ridley is an interesting case. He was not even near the planet when Kraid was defeated, only just landing on it when Samus reaches his hideout. In Super Metroid, he plays this pretty much straight, for both encounters.
 * Hoist by His Own Petard: Mother Brain attempts to finish off Samus with the Hyper Beam at the end of Super Metroid. Before dying, the infant Metroid steals it from her and gives it to Samus...
 * Also the Space Pirates in the remake portion of Zero Mission. Turns out the reason Tourian is empty is because the Metroids they were producing got loose and killed them all.
 * Hopeless Boss Fight: First fight against Ridley in Super; you can sort of win, as he fumbles the hatchling if you hit him enough times, but he still takes off with it after.
 * Not to mention the Super Metroid Final Boss, which can only be won -- and yes, it's possible to fumble it and LOSE during this fight. And SA-X before Metroid Fusion's finale. And the Giant Metroid in Super Metroid.
 * The Horde - The Space Pirate Confederation
 * Hot Amazon: Over six feet tall, clad head to toe in armour, and the biggest Badass in Nintendo's arsenal. Why don't we see more like her?
 * Hub Level: The Main Deck in Fusion and the Temple grounds in Metroid Prime 2: Echoes.
 * Humiliation Conga: By the time the end credits for Super Metroid start scrolling, Ridley has been blown up, Mother Brain has been blasted to oblivion and crumbled to dust, all of the Metroids are gone, and the space pirate base (all of it) has been vaporized in a planetary apocalypse.
 * I Am Not Shazam: People who refer to Samus as "Metroid".
 * In-universe, however, it's ironically fitting, considering that she has Metroid DNA in her as of Fusion. Also, Metroid is apparently the Chozo word for "Ulitmate Warrior" (or something along those lines). Which is pretty much what Samus is.
 * An Ice Person: Samus, considering all the ice power-ups. She gets this affinity turned around on her in Metroid Fusion; because she has Metroid DNA, cold becomes her greatest weakness. The organism in her old suit, the SA-X, uses her old ice beam to devastating effect whenever she bumps into Samus.
 * In Case of Boss Fight Break Glass: ... well, how else are you going to Attack Mother Brain's Brain?
 * Insectoid Aliens: The "Ki-Hunter" pirates of Super Metroid, Fusion, and Other M.
 * The main Space Pirate species as well, particularly in the Prime series but still obvious in the main games. Metroids have some insectoid features as well, especially in their "natural" life cycle.
 * In-Series Nickname: To space pirates, Samus is The Hunter.
 * Interquel: All of the games released after Fusion, though their exact placement in the timeline varies.
 * Interspecies Adoption: Samus was raised by the Chozo, who also taught her everything she knows as a bounty hunter.
 * Irish Names: Both "Samus" and "Aran" are generally Irish in origin. Samus being a female variant of James and Aran being a group of islands near the West coast of Ireland.
 * It's Personal: Just read the manga and you'll see that Samus has quite the bone to pick with the Space Pirates, Ridley, and Mother Brain.
 * Joker Immunity: Ridley will not stay dead, even if a planet is blown up under his feet.
 * The Juggernaut: The SA-X in Fusion is absolutely unstoppable until the end of the game. Just run.
 * Just Following Orders: Inverted; Samus, a bounty hunter, usually gets orders to the effect of "investigate X" and does everything else under her own steam.
 * Taken a step further in Fusion, where disobeying orders is actually part of the plot.
 * Kill It with Ice: The titular monsters, annoying as hell before you get some weapons effective against them. Though not as much with some of their later forms, the games rarely throw those at you
 * Last of His Kind: Super Metroid features the last Metroid. Samus herself might even count, given that, although human, she's carrying the DNA of the practically-to-totally extinct Chozo race.
 * Late Arrival Spoiler: The ending of Super Metroid is spoiled in the opening cutscene of Other M. Then again, it's one of the most iconic games in the series, so odds are a new arrival looking up Metroid info has already stumbled across it on a message board or something anyway.
 * Late to the Party: Fusion.
 * Latex Space Suit: Zero Suit Samus.
 * Lava Is Boiling Kool-Aid: In the original Metroid, lava was a red palette swap of acid.
 * While later games make lava a lot more realistic, Samus is still able to dive in it. This is justified by her suit most likely being more dense. In addition, the lava-proof Gravity Suit is a device whose primary function is to treat liquid as air, so by the time she's completely protected against lava, she should have no problem at all submerging in it.
 * Left Hanging: Some people are a bit annoyed at the lack of a sequel to Fusion, in no small part because the ending to that game addressed but didn't resolve a little factoid: And then they spend the next near-decade making prequels. Is it a little too much to ask for a game about this, Nintendo?
 * Lego Genetics: Samus is a human being genetically enhanced by Chozo blood. By Fusion, she's also part-Metroid.
 * Leitmotif: Ridley, ever since Super, has his own boss music, a remix of his/Draygon's/Torizo's/the escape theme from Super.
 * The SA-X also has its own distinctive theme music.
 * Samus herself, of course, has Appearance.
 * The Brinstar Theme has become rather iconic in its own right, despite not necessarily being the main theme of the game.
 * Lethal Lava Land: Present in some form in every Metroid game.
 * Le Parkour: Samus can do it in every game except Prime, and that may count too because she still has awesome cutscene moves.
 * Load-Bearing Boss: At least one in every game which will inevitably result in the destruction of a nearby planet (if not the planet under Samus' feet).
 * ...except Metroid II. At least, during the course of the game...
 * Lowered Monster Difficulty: The titular creatures are the scourge of the universe in Metroid and Super Metroid, needing to be frozen and pelted with missiles to kill. Through the Prime series, they become progressively less of an actual threat. In Prime 2, they can be beaten with enough firepower from any of your weapons, and in Prime 3, you eventually get the ability to kill them in one shot. Until then, though...
 * Possibly justified; the Metroids in the Prime games are a different strain (Tallon Metroids) that have been horribly mutated by massive, repeated exposure to Phazon. The SR388 and Zebes strains, on the other hand, are only vulnerable to cold until late in their life cycle.
 * Possibly justified; the Metroids in the Prime games are a different strain (Tallon Metroids) that have been horribly mutated by massive, repeated exposure to Phazon. The SR388 and Zebes strains, on the other hand, are only vulnerable to cold until late in their life cycle.

M-T

 * Malevolent Architecture
 * Mama Bear: The in Super Metroid results in an asskicking so epic that the Space Pirates refer to Samus Aran as "She Who Must Not Be Named."
 * Meaningful Name: To paraphrase The Other Wiki, Samus is the female variant of the name Seamus, which is celtic for James and means "One who supplants." Her last name, Aran, is the name of an island. One who supplants an island, or One who conquers isolated territory by force.
 * Perhaps also, one who is an island, in a metaphorical sense -- one who is isolated, existing and subsisting as an entity unto herself. Samus does pretty much always operate alone, without any outside aid or companionship (except for briefly in the beginning of Corruption.
 * Metamorphosis Monster: While on their home planet at least, the Metroids go from floating parasitic jellyfish to beetlelike creatures to giant armored lizards. In an interesting twist, the first stage is not only the most well-known and arguably most dangerous, but while nearly every game has a variant of the jellyfish stage, the later stages have only appeared in a handful of games.
 * Metroidvania: Pretty much started and codified the genre.
 * Minus World: In the NES original and Game Boy sequel.
 * Mistaken for Granite: The first Chozo Statue in Super Metroid seems inanimate until you take the powerup it holds and try to leave, at which point the exit seals and it attacks you.
 * Multiple Endings: The Segmented Endings subtrope, whether based on completion time or percentage.
 * Nice Job Breaking It, Hero: Samus' Metroid extermination campaign caused an explosion in the population of the X Parasites, which the Metroids had been designed to kill. Oops.
 * Ninja Pirate Zombie Robot: Ridley started as a dragon space pirate, and adds more to this title in the Prime games, culminating in him being a mutant zombie cyborg dragon space pirate.
 * In Super, there are two gray Space Pirates that fight by using martial arts, which were called "Ninja Pirates" by fans.
 * Nintendo Hard: Geting 100% without a guide is hard, doing that while beating it in under 2 hours is even harder. If this is you first time playing any particular game, be you a veteren or a newcomer, you WILL die at least 20 times. Now try and get 100% under 2 hours without dying on hard mode!
 * No-Holds-Barred Beatdown: Samus to Mother Brain during the mother of all Mama Bear moments at the end of Super Metroid. After what Mother Brain did, she completely deserved it.
 * Noob Bridge: The Trope Namer is a crumbling bridge encountered early in Brinstar in Super Metroid, and the first place in the game that would require any player (of less than insanely good skill) to use the run button. The run button, however, is not part of a standard control scheme even within the Metroid series. Many newbies get stuck there, unaware of the otherwise obvious solution.
 * No Transhumanism Allowed: One of the rare and surprising aversions: not only are cybernetics commonplace and carry no notable social stigma, Samus herself is a transgenic lifeform, with her adoptive Chozo caretakers having grafted their species' DNA onto her own to increase her adaptability to the harsh environment of Planet Zebes. Further, by the end of Metroid Fusion, Samus is also, and that's not even getting INTO her brushes with Phazon...
 * Not to mention,.
 * Ominous Latin Chanting: Lower Norfair... and it's awesome.
 * One-Hit Polykill: The plasma beam works this way.
 * One-Winged Angel: SA-X, though it later turns into a gigantic hulking monster that can be defeated with three charged shots. Just don't let it hit you.
 * One Woman Army: The Galactic Federation staged an all-out attack on the Space Pirate base on Zebes. When that didn't work, they sent Samus.
 * Opening the Sandbox: Fusion is the most linear game in the series yet, and thus has very few opportunities to let you backtrack to earlier sectors on your own until the endgame.
 * Our Monsters Are Weird: The titular Metroids.
 * Palette Swap
 * Perfect Pacifist People: The Chozo have evolved to a point in which they live in harmony with nature, shunning violence and destructive technology. Of course, they were warriors once, and were able to create the advanced armor that Samus uses.
 * Personal Space Invader: The titular Metroids.
 * Pinball Spinoff: Metroid Prime Pinball.
 * The Pirates Who Don't Do Anything: Arguably the Space Pirates, who often are found in lairs breeding bioweapons but rarely found actually committing piracy.
 * Justified in that Samus is usually sent in to pirate lairs post-piracy. You can see the pirates in action in the opening sequence of Super Metroid, when Ridley pirates the last metroid from the research station. Presumably, pangalactic police prevent protracted piratical processes, only summoning up their favourite bounty hunter to go in and blow up the place when they track down the actual lair -- which would probably be largely immune to a head-on raid by federation forces.
 * The Pirates did quite a bit of pirating in Prime 3: Corruption, in which they hijacked an entire Federation battleship (GFS Valhalla), murdered its crew, and stole its onboard Aurora Unit. Later, they tried to pull the same trick against the GFS Olympus. They didn't count on The Hunter being aboard...
 * Plug N Play Technology: Samus' suit is described to be "modular", which means it can also identify other technologies and adapt them into itself. The suit is able to form new abilities just by absorbing "data" acquired from rooms and the DNA of the X parasites in Fusion.
 * Subverted in Zero Mission, where you find a few upgrades incompatible with your suit.
 * Point of No Return: Once you've saved at the second save point in Tourian in Super Metroid, you can never go back. You're never told this.
 * Posthumous Character: Adam Malkovich is technically this, although Fusion puts an odd spin on it. Other M, which takes place before Fusion, will show him before his death.
 * Power Crystal: The Lensman-like hand crystal on the back of her left hand. Originally just a visual effect, Zero Mission made it integral to use of the Power Grip, and Metroid Prime 3: Corruption has it as the source of the Grapple Beam.
 * Powered Armor: Samus' suit.
 * Puzzle Boss: Many, including Crocomire.
 * Puzzle Pan
 * Raised by Natives: Samus.
 * Rasputinian Death: Crocomire in Super Metroid.
 * Recurring Boss: SA-X in Fusion, though it's not really a boss until near the end of the game. Ridley may be a better example, considering he appears in almost every game, and twice in Corruption. Also,.
 * Remember the New Guy?: In the E 3 2009 trailer for Metroid: Other M, a Power Armor-clad man greets Samus and says "Remember me?", opening his visor. Samus may have, but Metroid fans did not. A meme was born.
 * Ridiculously Cute Critter: In the manga, Samus' pet Ponchi appears to be about half squirrel, half rabbit, and all adorable. Also, the Etecoons and the Dachoras in Super and Fusion. Played with the Little Birdie in Other M, which turns out to be a Killer Rabbit.
 * Roar Before Beating: Some of the bosses do this.
 * Roaring Rampage of Revenge: In Super Metroid.
 * This could also be seen as one of Samus' main motivations, especially against Ridley, who personally killed her mother right in front of her when she was four years old. The entire series could be seen as a bit of this trope against the Space Pirates and Ridley.
 * While all of Super Metroid is a Roaring Rampage of Revenge, the last bits of Metroid: Zero Mission are as well.
 * Run, Don't Walk: Super has a run button, which is even the basis for the infamous "n00b bridge".
 * Samus Is a Girl: Duh.
 * Sand Is Water: In Maridia, when the Gravity Suit is acquired, water no longer renders Samus sluggish. However, flowing sand pits underwater still slow her down.
 * Savage Setpiece: Multiple non-hostile indigenous creatures will turn into this if you attack them.
 * Save Point: The second type is a common sight in the series starting with the second game; the first game used passwords instead. With the exception of Chozodia save points in Zero Mission and Samus's gunship, they never refill health. The Save Stations in the Prime series, however, save and heal.
 * Scenery Gorn: Old Tourian in Super, in Metroid Fusion.
 * Schematized Prop: Many of the more recent games have taken up this trope, most notably using a Power Suit schematic as the item/weapon status screen (Zero Mission, Prime, Prime 3, Super, Fusion; the schematized suit was also seen in the instruction manual for Metroid II).
 * Sci-Fi Writers Have No Sense of Scale: Very few of Samus's weapons have numbers behind them, but those that do are absurdly powerful -- like "fully automatic nuclear explosion launcher" powerful.
 * Sea Monster: The boss Serris is a sea serpent with Super Speed. Before Serris, there was Super miniboss Botwoon, who was a serpent like Serris who sped up as he took damage, and could spit acid spread-shots.
 * There's also Draygon, the boss of Maridia.
 * Sequel Hook: Fusion sure seemed to leave one hell of a sequel hook, what with
 * A sequel on the DS with 2-D gameplay, Metroid Dread, was supposed to have been shown at E 3 2006, but was mysteriously dropped. Potentially hinted at again in Corruption, however.
 * Sequence Breaking: Possibly one of the most well-known examples.
 * Even after seventeen years, people are still discovering new tricks like this. (See 14:55 in the video)
 * Shapeshifter Baggage: No attempt is made to explain where Samus stuffs the rest of her body when she assumes Morph Ball form. The games say it is about a meter in diameter, but the visual size is arguably smaller than that. X parasites are another example, morphing from single cells to monstrous creatures instantly.
 * Even Lampshaded in-game when the Space Pirates tried to copy the Morph Ball technology, and ending up breaking every bone in the test subjects' bodies.
 * The Prime series depicts her as being turned into energy when in ball form. How she sees is not explained.
 * Shark Tunnel: These are a common feature in the newer games, starting with the tunnel between Brinstar and Maridia in Super Metroid, and including the underwater tunnel in Sector 4 in Fusion, the skywalk between Chozodia and the Pirate Mothership in Zero Mission, and the skywalk from Magmoor to Phazon Mines in Prime. All of them can be shattered with power bombs to allow free travel between the two areas.
 * She's Back: In Zero Mission. After ? Running and hiding from just about everything. After ? The Hunter, who sends waves of terror throughout the Space Pirate legions, is reborn, more powerful than ever.
 * Hell, the first thing you do when you get your suit back is clear a small group of Pirates in one shot with your shiny new Plasma Beam. Revenge is sweet >:3
 * Shifting Sand Land: Sector 3 - PYR.
 * There's also the Agon Wastes in Echoes and the Experimental Simulated Desert in Other M.
 * Shoulders of Doom: The Varia Suit adds them.
 * Shout-Out: Several to the Alien franchise. Ridley is named after director Ridley Scott, and the opening shot of Prime is almost identical to that of the first film. Even the title logos have similarities (ALIEN - メトロイド).
 * A non-enemy creature in Super Metroid has a turtle like shell that flies around while spinning. Likely a nod to Gamera. Or possibly Bowser.
 * Its offspring look strikingly similar to Buzzy Beetles.
 * A blink-and-you'll-miss-it example is the name of the planet that houses one Federation shipyard, where the GFS Olympus and Samus' gunship (the one used in Prime 2; she goes through gunships like other people go through tissues) were built: Aliehs III.
 * And then there's the fact that, as of Super Metroid, Samus can SHIIIIINESPAAAAAAAARK!
 * Houston from the Super Metroid Comic in Nintendo Power seems to refer to Captain Dallas from the first Alien film.
 * In-universe example:
 * The original Famicom Disk System version of the first game's Escape theme and subsequent arrangements in future games don't have it, but the NES version features a slight expansion that includes a recurring six-note melody from the Kid Icarus soundtrack.
 * Moonwalking in Super Metroid.
 * Outside the actual series, in Super Smash Bros. Brawl, one of Zero Suit Samus' air-attacks is the Inazuma Kick from the Gunbuster-series.
 * Slippy-Slidey Ice World: Sector 5 - ARC.
 * There's also the Cryosphere in Other M and the Phendrana Drifts in Prime.
 * Sole Survivor: Samus, twice over: first when the K-2L colony was slaughtered by the Space Pirates, and again when the Space Pirates, under Mother Brain's direction, invaded Zebes and killed the remaining Chozo. Well, on Zebes, anyway. And then there's the last remaining Metroid from Metroid II.
 * Something Completely Different: Metroid Prime Pinball qualifies.
 * Space Pirates: The primary antagonists for most of the series; only three games didn't have them as the main attackers, and in two of the three, they made cameo appearances anyways.
 * Space Marines: In Prime. Space Army in Other M. Both are Badass, just not as badass as Samus.
 * Samus herself had once been a Space Marine when she was serving under Commander Adam Malkovitch.
 * Speed Run: Super Metroid and the following sequels have their maps designed so that you can solve them in a fraction of the expected solving time by using special techniques like wall jumping, bomb jumping, mock ball, etc. to get key items ahead of time.
 * Sprint Shoes: Speed Booster.
 * Starfish Aliens: The main ones are X Parasites, the Ing, and Metroids, but others tend to pop up.
 * Statuesque Stunner: Samus.
 * Stealth Based Mission: Infiltrating the Space Pirate Mother Ship in Zero Mission.
 * Sub Boss: Return of Samus is the only game that doesn't have at least one.
 * The tougher Metroids in that one could qualify.
 * Suddenly Voiced: In Brawl, Samus finally spoke her taunts. However, they sounded rather... odd. In Other M, she speaks for the first time in her own series.
 * Superweapon Surprise: Don't mess with Chozo statues... just, don't: "Those who defile [our statues] shall know our wrath, unfettered and raw."
 * In addition to that: do you know what you get when the peaceful, spiritual race bird race actually trains someone to fight, and gives them the technology to do so? You get Samus Aran.
 * And there used to be many more just like her (albeit Chozo). Samus is referred to as the first "Chozo" in many generations to choose the path of the warrior.
 * Survival Horror: Metroid Fusion will never be confused with Silent Hill 2, but the claustrophobic environment, the strictly linear gameplay, the profusion of locked doors, and the relentless pursuit by an invincible enemy give the two games an uncanny resemblance.
 * Suspicious Videogame Generosity: If there is a save station -- and possibly recharge room -- next to a huge room, expect a boss to be nearby...
 * Swiss Army Weapon: Samus' cannon shoots various beams, including power, ice, plasma, and wave, and also missiles.
 * Hell, the whole Power Suit could be a Swiss Army Outfit.
 * Sympathy for the Devil: As the series goes on, you realize the Metroids aren't so bad -- this culminates with Samus becoming part-Metroid in Fusion.
 * In Other M, maybe
 * Techno Wreckage: The Wrecked Ship in Super Metroid.
 * Temple of Doom: Chozodia.
 * Theme Music Power-Up: This occurs in every Metroid, but perhaps the most gratifying moment is in Zero Mission when, after running for your life from Space Pirates with nothing but your Emergency Pistol and defeating the Chozo Ghost, Samus' unknown items transform into the Plasma Beam, Gravity Suit, and Space Jump Boots. At this point, you can finally kill the Space Pirates, and with ease I might add.
 * The Galactic Federation
 * Tomato Surprise: See Samus Is a Girl above.
 * Took a Level In Badass: In Super Metroid, Samus' surrogate Metroid child returns.
 * In most games, the Ice Beam is a useful weapon, but not that powerful. In Metroid Fusion, Samus develops a weakness to cold and loses the Ice Beam. It becomes a weapon of pure murder when used against her, and
 * Trauma-Induced Amnesia:
 * Turtle Power -- The oft-forgotten and turtle-like Tatori and Tatori, Jr. creatures in Maridia are non-hostile toward Samus; Tatori even lets Samus stand on top of it to access an Energy Tank and a Missile Expansion.

U-Z

 * The Undead: Coverns (Three skulls stuck together), Phantoon (Huge malevolent spirit allied with the Pirates), Chozo Ghosts, Dark Marines, and Skeleton Crocomire.
 * Underground Level: The setting of a good majority of Super Metroid.
 * All of the action in Metroid II takes place in the caverns of SR388. The only part of the surface the player sees is the immediate area around Samus' ship, and the hills behind it at the end of the game.
 * The first Metroid is entirely underground as well. Most of the games have significant amounts of this.
 * Unexpected Gameplay Change: Stealth after Samus loses her suit in Zero Mission.
 * Unique Enemy: Used frequently beginning with the 16-bit installments, especially Super Metroid.
 * The Very Definitely Final Dungeon: The Final Boss is always in an impressive location:
 * The original puts Samus in
 * Metroid II has
 * Super Metroid takes us
 * Fusion ends things
 * Prime ends in
 * Zero Mission has Samus infiltrate
 * Echoes finishes up in
 * Hunters gives us
 * In what may be the most over-the-top instance of this trope in the series, Corruption
 * And to finish things off, Other M
 * Victor Gains Loser's Powers:
 * Samus in Metroid Fusion had all her abilities copied by X. After killing X-infected bosses (which tend to be able to produce similar attacks), she can absorb the X-parasite to regain that power.
 * Metroid Prime 2 does something similar, where, after losing most of her starting abilities to a mob of Ing, she has to regain them in one-on-one boss battles where they're used against her.
 * In Zero Mission, Samus somehow gets the Charge Beam this way, even though her opponent, Deorem (A.K.A the "Charge Beam Beast"), never used anything like it. Metroid Prime also has a few examples, such as the Varia Suit from Flaaghra, the Spider Ball from Thardus, and the Phazon Suit from the Omega Pirate. Metroid Prime 3 has Samus gain the Ice Missiles, Plasma Beam, Grapple Voltage, and all the Phazon upgrades this way.
 * Video Game Remake: Zero Mission.
 * Villain Based Franchise: Fusion more or less Inverts this, giving Samus herself Metroid-DNA.
 * Wall Jump: Starting with Super Metroid, Samus quickly became one of the most notable employers of this technique. It also is the primary tool of sequence breakers.
 * Prime 2 was the first game that explicitly informed the player that this was one of Samus' abilities; in all previous games, it was a secret, and admittedly optional, technique.
 * What Measure Is a Non-Human?: Averted in Metroid II. Samus couldn't bring herself to kill a child, even if said child was a parasitic monster and a potential threat to the galaxy. It certainly helped matters that she felt an attachment to the creature.
 * Wolverine Publicity: The Varia Suit is used in almost all of the series' covers and promotional images, even though it's typically only the middle of three suits.
 * Womb Level: The innards of the Leviathans in "Prime 3", though that's more of a case of 'Womb Boss Chamber'. Phaaze is a living planet, too, though only a few parts of what we see of Phaaze is definitely organic.
 * You Don't Look Like You: Samus herself suffered this problem until about Metroid Zero Mission. She was usually a blonde -- except when her hair was brown, green, or Dark Skinned Purple -- and her various facial features and overall style of rendering fluctuated somewhat. However, once Zero Mission/Prime 2 hit, her appearance seemed to standardize.)
 * Her armor also changed drastically between Metroid 1 and 2, and all flashbacks to the first game depict the redesigned armor. It got a further redesign in Metroid: Other M, which is also depicted in flashbacks to Metroid 2 and Super Metroid.
 * Ironically, Samus in Fusion doesn't look much like her retcon-ed self in any of the other games, though considering she had some major sugery and DNA transfusion in said game...
 * Younger Than They Look: According to the official tie-in manga, Samus is only supposed to be 17 during the events of the first game, but most fans have their doubts about that.
 * Your Princess Is in Another Castle: You've defeated Mother Brain and escaped Zebes in Zero Mission... the game is over, right? Though, you never did find out what those mysterious power-ups were for...
 * Zeerust: It's not really apparent in-game, given the low graphical capabilities of the console and the general lack of technology aside from Samus' suit, the doors, and the elevators, but the artwork of Samus for the original NES game makes it very apparent that Metroid was made in The Eighties. It has a rather boxier look than later portrayals, for one thing. Later games aged much better in this regard: even the immediate sequel to the first game, which was released only a few years later, features an artwork design for Samus that still looks pretty good even after twenty years.
 * Zip Mode: Samus' Speed Boost could be considered this if having to trek along a long straight path; she will travel fast enough to kill all normal enemies in the way.
 * Zombie Apocalypse: The BSL station succumbs to one courtesy of the X Parasites. It's a small taste of what could have happened to the entire galaxy had they got off the station.