Sonic 3 and Knuckles



Sega's third 16-bit entry in the Sonic the Hedgehog series, and the followup to the wildly popular Sonic the Hedgehog 2, was so epic that time and hardware constraints forced them to split it into two separate games:

Sonic the Hedgehog 3, released February 2, 1994, covered the first half of the game, with gameplay as Sonic, Tails, or both. Knuckles the Echidna, the final member of Sonic and Tails' Power Trio, made his debut in this game, but as an antagonist rather than a playable character.

Sonic & Knuckles, released October 17th that same year, covered the second half of the game, including Knuckles' Heel Face Turn, and allowed gameplay as either title character (but not Tails).

The game also featured "Lock-on Technology"--a slot on top of the cartridge, in which another Mega Drive / Genesis cartridge could be inserted. By connecting the Sonic 3 and Sonic & Knuckles cartridges this way, the two could be played as one complete story, Sonic 3 & Knuckles, with all three characters playable for the entirety, as was originally intended.

When playing as Sonic or Tails, the plot picks up right where the Genesis Sonic 2 left off. Dr. Ivo "Eggman" Robotnik's Death Egg, just recently destroyed by Sonic, crash lands on the mysterious Angel Island (or Floating Island, as the American game manuals called it). Sonic and Tails follow, intending to stop Robotnik from rebuilding the Death Egg. Not one minute after landing, Sonic gets a face full of fist, courtesy of the island's native inhabitant: Knuckles, the last surviving Echidna and protector of the Master Emerald whose power keeps Angel Island aloft. Knuckles is convinced that Sonic is a thief who intends to steal said Emerald. Why? Because Robotnik told him.

So while Sonic and Tails thwart Robotnik, Knuckles waylays them with traps and all around acts as a thorn in their side. This finally comes to a head when everyone reaches the Hidden Palace: Robotnik steals the Master Emerald and electrocutes Knuckles for trying to stop him. Knuckles realizes he's been had, and immediately joins Team Sonic, showing them how to get out of the Hidden Palace and onto the Death Egg.

The plot of Knuckles' game covers most of the same levels as Sonic's, and features Knuckles fighting one of Robotnik's EggRobos--rather than the Doc himself--piloting souped-up versions of the level bosses. This culminates with a battle in the clouds against a Master Emerald-powered Mecha Sonic. It's a bit unclear when this all occurs in relation to the plot of Sonic's game. Official sources, such as the game manuals, imply that both plots occur simultaneously. However, in-game details appear to contradict this, and suggest that Knuckles' plot begins shortly after the end of Sonic's plot.

The gameplay represented further Sequel Escalation compared to Sonic 2: The top speeds were even faster, the levels were even larger, and for the first time every Act featured a boss fight. There was more focus on plot as well--Knuckles' antagonism towards Sonic and Tails was shown through a number of in-level, wordless cut scenes, and every level ends with a brief scene of the characters traveling to the next level.

A number of game mechanics made their Sonic debut here as well, such as a game save feature and specialized shields. The Special Stages from Sonic 2, where the Chaos Emeralds could be won, were revamped, and three different Bonus Stages were introduced, where extra rings and powerups could be collected. Cast Speciation (first introduced in the previous year's 8-bit title Sonic Chaos) was further developed: Sonic could make use of a brief, midair "Insta-Shield", and do a special attack while having one of the shields (a double-jump with the lightning shield, a bounce attack with the bubble shield, a fiery charge attack with the fire shield); Tails could fly (by himself or while carrying Sonic) and swim; and Knuckles could glide and climb sheer walls, but couldn't run as fast or jump as high as Sonic.

Sonic & Knuckles' lock-on technology also worked with the Sonic the Hedgehog 2 cartridge, allowing you to play Knuckles the Echidna in Sonic the Hedgehog 2. The developers attempted to implement a similar feature with the original Sonic the Hedgehog, but found that Knuckles' color palette was incompatible with the game's (though a fan hack eventually proved that Knuckles could indeed be implemented in Sonic 1). Instead, combining the two cartridges gives you the Blue Sphere minigame, with many, many, many, many, many, many (did we mention many?) variations on the Special Stage.

Sonic the Hedgehog 4, is a direct follow-up to this game, though the Excuse Plot of Episode I doesn't suggest it.


 * Action Bomb: Iwamodoki
 * Advancing Boss of Doom / Advancing Wall of Doom / Descending Ceiling / Auto-Scrolling Level / Get Back Here Boss / Rise to the Challenge: There's a higher concentration of "keep moving or die!" scenes here than in any other Sonic game.
 * The auto scrolling scene with the bomber airship in Angel Island Zone Act 2.
 * The wall of doom in Hydrocity Zone Act 2.
 * The collapsing ceiling/rising floor/whatever the hell Eggman's drill-mech does to the landscape in Marble Garden Zone Act 2.
 * The rising water level in Knuckles' version of Launch Base Zone Act 2.
 * The auto scrolling boss fight in Mushroom Hill Zone Act 2(And the page image for Get Back Here Boss).
 * The crumbling airship in Flying Battery Zone Act 2.
 * The rising sand sequences in Sandopolis Zone Act 2. The boss of the level is an advancing sphinx-mecha, which crushes you against a wall if you take too long to defeat it.
 * The pre-boss fight forced-scrolling scene in Lava Reef Zone Act 2.
 * Robotnik's screen-filling, inexorably advancing mecha in Death Egg Zone Act 2. After defeating it, you chase Robotnik's Eggmobile, carrying the Master Emerald, while the platform collapses behind you.
 * The entirety of The Doomsday Zone.
 * One of the three bonus levels features this, with a glowing, upward-climbing double helix that ends the level if you touch it.
 * Airborne Aircraft Carrier: Flying Battery Zone; the Flying Battery also tries to bomb Sonic in Angel Island Zone.
 * Airborne Mook: Caterkiller, Jr., Buggernaut, Jawz, Bubbles, Batbot, Star Pointer, Flybot767, Orbinaut, Butterdroid, Dragonfly, Hyudoro, Fireworm, Eggrobo, Spikebonker, and Chainspike.
 * Always Over the Shoulder: The bonus stages.
 * Amusement Park of Doom: Carnival Night Zone. Also, Balloon Park from the 2-player mode.
 * This is very literal in the minds of many when you consider THAT DAMN BARREL!
 * Ancient Egypt: Sandopolis Zone is Ancient Egypt ON THE FLOATING ISLAND!
 * And I Must Scream: Subverted: when you beat the Lava Reef Zone boss, Eggman sinks into the lava, which cools and hardens seconds later. After the Knuckles fight in Hidden Palace Zone, he's shown to be perfectly fine.
 * Another Side Another Story: ...Maybe. It's hard to tell, given the minimalist style of 16-bit-era storytelling, but Knuckles' adventure might actually take place after Sonic's; see here for an analysis.
 * Background Boss: The first part of the final boss.
 * Bag of Spilling: The good ending of Sonic 2 is used as the canon one, with the opening cutscene showing Super Sonic briefly before Knuckles punches the emeralds out of him and takes them away.
 * Bait and Switch Boss: Knuckles's version of Sky Sanctuary opens with the EggRobo attacking... but then Mecha Sonic (unintentionally) destroys it, and you fight the Evil Knockoff of Sonic instead.
 * Batman Can Breathe in Space: Death Egg Zone Act 2, and Doomsday Zone.
 * Because Destiny Says So: The mosaics in the background of Hidden Palace Zone are clearly a stylized depiction of Hyper Sonic's fight with the final boss.
 * Bedsheet Ghost: In Sandopolis Zone Act 2.
 * Berserk Button: The second stage of the Death Egg Zone's miniboss seems to have one: it will start spinning a pair of spiked platforms extremely rapidly while firing off a massive laser beam if you attack it.
 * Big Boo's Haunt: Act 2 of Sandopolis; the ghosts will pester you (eventually hurting you) constantly if you don't keep the lights on.
 * Blackout Basement: Carnival Night Zone Act 2 (for Sonic and Tails), and Sandopolis Zone Act 2.
 * Bonus Stage: Unique among Sonic games for having two types:
 * "Special Stages:" A 3D maze where you must "Get Blue Spheres". Finishing earns you a Chaos Emerald. Accessible via giant rings hidden in the levels.
 * "Bonus Stages:" Stages for collecting rings and powerups. Accessible via a circle of stars that appear if you pass a star post with 20 or more rings.
 * Boss Only Level: The Doomsday Zone.
 * The Great Eggman Robo may also count, as it seems to be in its own act.
 * Boss Rush: Sky Sanctuary Zone.
 * Bottomless Pit Rescue Service: With the Marble Garden Zone boss, due to the nature of the battle.
 * Brick Joke: As you run through Launch Base Act 1, you'll eventually find Dr. Robotnik carrying some sort of box around. That's the stage's Mid-Boss. When you defeat it, you might notice there are another two boxes in the wall. Those are the ones Knuckles will later fight in his version of the level.
 * Build Like an Egyptian: Sandopolis Zone Act 2.
 * Cast Speciation
 * Comic Book Adaptation: In both Sonic comics:
 * The Archie comic had a short adaptation of Sonic 3 in issue #13, and also a 48-page special based on Sonic & Knuckles. Neither story actually featured the Death Egg (as that was saved for a later mini-series).
 * Sonic the Comic had Robotnik's second Death Egg being stuck on the Floating Island for the span of about 19 issues, the first four of which adapted the plot of Sonic 3, and the last five of which were based on the closing levels of Sonic & Knuckles.
 * Continue Your Mission, Dammit!: See Idle Animation.
 * Also, after Knuckles lowers the bridge for you in Sky Sanctuary, ducking next to him makes him look at your character and wave his arm, as if telling you to go on without him.
 * And, in Sonic's continue screen, Tails tugs at his arm while pointing forwards.
 * Convection, Schmonvection: Two-thirds of Angel Island Zone is in the middle of a massive forest fire, yet the characters don't seem to mind. And naturally, Lava Reef Zone's lava only hurts you if you actually touch it.
 * Of course, you can stand on the lava just fine if you have a fire shield, even stand in a lava waterfall.
 * Conveyor Belt O' Doom: Death Egg Zone has elevators with conveyor belts that randomly switch direction and try to force Sonic into spikes or gun turrets.
 * The Dev Team Thinks of Everything: Most of the environmental hazards of the game can be rendered harmless with the right shield. Lava Reef Zone is obviously best played with the flame shield, whereas the lightning shield becomes extremely useful for running safely on the electrified floors and ceilings of Death Egg Zone.
 * Difficult but Awesome: The instashield of Sonic's. Slightly increases the range at which you can hurt enemies, and allows you to phase though things like projectiles, invincible enemies and other terrain hazards. It only lasts a split second though, so good timing is an absolute must.
 * Difficulty by Acceleration: Used in the bonus stages.
 * Divergent Character Evolution: Tails played like a Palette Swapped Sonic in the last game. He begins to diverge here; his speed and jump height have been reduced ever-so-slightly compared to Sonic, but players can now control his ability to fly. Although as a trade-off to this awesome ability, Tails can't take full advantage of the shields (i.e. the extra jumps they give Sonic) and he doesn't go super until he collects both the chaos emeralds and the super emeralds.
 * Dual Boss: The Launch Base Mini Boss for Knuckles.
 * Dummied Out: Much of Knuckles' content is present in the Sonic 3 cartridge, but can't be accessed without attaching it to the Sonic & Knuckles cartridge. Also happens in reverse: In the combined game, when you play Launch Base Zone (the final level of Sonic 3) as Sonic or Tails, the game skips over the original final boss of the level (including the awesome ending music, sniff). Though you do still fight it if you play as Knuckles.
 * The standalone Sonic 3 cartridge has the S & K miniboss music dummied out, you can hear it during the Hydrocity Act 1 boss fight if you wait until the drowning music starts, then jump out of the water.
 * Another reversed example: The infinite oxygen of the bubble shield is useless in the standalone Sonic & Knuckles, as it does not contain a single underwater section.
 * The S&K music is also in the S3 cartridge...all of it. In the sound test, most of the zone music that exists in track 09 onward is from S&K. So its dummied out in that its not used but its still in the cartridge.
 * Eleventh-Hour Superpower: Sonic goes into Super Mode to fight the Perfect Run Final Boss. Though it's less of an Ass Pull, because the player could use the same super mode in any earlier level of the game, and the requirements to fight it are collecting all of the Green Rocks that let you turn into Super Mode. In most subsequent games, the Super Mode is only used for True Final Bosses.
 * Endless Game: Blue Sphere.
 * Eternal Engine: Flying Battery Zone, Death Egg Zone. Also Chrome Gadget from the 2-player mode.
 * Every Fifty Thousand Points: You are awarded an extra life every 50,000 points.
 * Everything Is Even Worse With Sharks: Inverted. The "Jawz" Mook you face in Hydrocity is arguably the easiest enemy to beat in the entire zone. It slowly propels itself horizontally from offscreen, and while it has a tendency to appear suddenly and in groups, it can be hit anywhere with a spin attack or jump attack. The inversion is that Jawz appears exclusively in the second act, while the much more bothersome Buggernaut appears exclusively in the first act. Hence, Hydrocity is actually better with sharks!
 * Evil Knockoff: Mecha Sonic. Ironically, in the first two fights he uses Robotnik's tactics by reusing boss machines from previous games. In Knuckles's playthrough he's the Man Behind the Man and final boss.
 * Foreshadowing: When fighting against Knuckles, there is a background mural depicting Robotnik/Eggman stealing the Master Emerald, and Hyper Sonic attempting to stop him. Guess what you have to do in the true final level?
 * Face Ship: The Death Egg, which has Eggman's face on it.
 * Floating Continent: The setting of the game, although it got knocked out of the sky by the Death Egg's crash landing prior to Sonic's arrival. It gets raised at the end of Sonic's story path and remains afloat throughout Knuckles's.
 * Fungus Humongous: Mushroom Hill Zone has mushrooms large enough to bounce on, use as a seesaw catapult, and parachute from.
 * Game Breaking Bug: Many. If you manage to kill the robot who flame the forest in the end of Angel Island Zone Act 1, Act 2 doesn't load the level layout.
 * Hyper Sonic is a virtual game breaking machine since the developers probably didn't full test him given that he was a last second throw-in for the 2 games being separated.
 * Gameplay and Story Segregation: After the Angel Island Zone is set on fire, there isn't really any dramatic change to the gameplay to indicate that the zone's on fire. No coming face-to-face with flaming walls or anything. It has basically no gameplay effect whatsoever, aside from one zip line that cuts off fairly quickly because a small section of it is burning halfway down.
 * Knuckles shuts off the lights in Carnival Night, but aside from raising the water level for all of 30 seconds, it seems to do nothing except show off how much of a prick he is.
 * Gotta Catch Em All: In Sonic 3, there are 7 Chaos Emeralds to collect, and getting all of them lets you use the first Super Mode (unless you're playing as Tails). Later, once you get to the Sonic & Knuckles levels, you can power up the gems into the Super Emeralds... and collect them again, for a total of 14 emeralds. Getting the second set lets you use your character's hyper form.
 * Gravity Screw: Used extensively in Death Egg Zone, as well as the anti-gravity platforms in Carnival Night.
 * Green Rocks / Mineral MacGuffin: The Master Emerald and the various Chaos Emeralds.
 * Guide Dang It: There is one point in Carnival Night Zone, Act 2, where a red-and-white barrel (the Barrel Of Doom!) is blocking the path. The only way to proceed is by standing on the barrel and pressing up and down on the D-pad as the barrel wobbles. There's nothing in the game itself to suggest this.
 * Hailfire Peaks:
 * Angel Island is equal parts Green Hill Zone and Jungle Japes. Only after a certain point it's ON FIRE.
 * Sandopolis Zone is a Haunted Temple of Doom in Shifting Sand Land.
 * Lava Reef Zone starts off as a straight volcano level, then in Act 2, the lava cools off and there's white crystals everywhere.
 * Sky Sanctuary is a castle floating among the Bubbly Clouds.
 * Hand Wave: What the instruction manual does in regards to certain glitches, where Mercy Invincibility could cause you to get stuck in certain places and be forced to reset the console, handwaving them as one of the "many diabolical traps" set up by Robotnik.
 * Harmless Freezing: Averted in Ice Cap Zone.
 * Hedgehog Cannonball: A common level feature in Carnival Night Zone.
 * Hero Antagonist: Knuckles, initially.
 * High Altitude Battle: All the final bosses.
 * Also, the boss of Marble Garden Zone Act 2, which is fought by having Tails fly Sonic to chase after it.
 * Homage: The item monitors strongly resemble Apple Macintosh computers.
 * Hoist by His Own Petard: This is how about half the bosses in Sonic & Knuckles are defeated.
 * Horrible Judge of Character: Knuckles believes Obviously Evil Eggman's claims that Sonic and Tails are the bad guys.
 * Hub Level: The area where the Master Emerald is kept becomes sort of a Hub Bonus Level when playing the second half of the linked game; entering a giant ring sends you there, where you can choose which Super Emerald you'll try to obtain.
 * Humongous Mecha: Robotnik uses one at the end of Sonic & Knuckles.
 * Idle Animation: As in the previous games, Sonic will look at the player and tap his foot impatiently if the player does nothing for several seconds, occasionally pointing in the direction he's currently facing.
 * Tails will stare at the player and occasionally yawn.
 * Knuckles will start boxing impatiently.
 * Immediate Sequel: To Sonic the Hedgehog 2
 * Inconveniently-Placed Conveyor Belt: Hydrocity Zone, Death Egg Zone.
 * Infinite 1-Ups: Those alarm lights that trigger flying enemies in Launch Base Zone. Hold down a spin dash in one of those alarms, and a constant stream of enemies will fly right into you and be destroyed. The score given for the chain of hits eventually results in one life being granted every 3 seconds, and even if you die by time out, since it's before the first checkpoint, you can just walk back there and do it again.
 * Invisible Wall: Appears in a cut scene in Carnival Night Act 2, and just before the first boss battle in Launch Base Act 2.
 * Jerkass: Knuckles, until Hidden Palace Zone.
 * Kill It with Fire: In Angel Island Zone, Robotnik tries to kill Sonic by firebombing the jungle.
 * Then at the end of Lava Reef, he uses the Death Egg's eye lasers to reignite the volcano with Sonic in the middle.
 * You can do this to enemies if Sonic has the flame shield and jumps twice.
 * Let's You and Him Fight: Knuckles vs. Sonic and Tails.
 * Lethal Lava Land: Lava Reef Zone.
 * Levels Take Flight: Flying Battery Zone features a few segments where the player must navigate the outside portions of Eggman's ship.
 * Load-Bearing Boss: The gigantic Eggman mecha at the end of Death Egg Zone. Makes sense, since it not only contains the power source for the whole station, but is also so darn huge that crash landing into the superstructure would certainly do the trick.
 * Logo Joke: In Sonic 3, the Sega logo remains in place as a blue ball blazes towards the camera before revealing itself to be Sonic, followed by a white flash that leads into the title screen. In Sonic & Knuckles, the Sega logo remains as the background turns into Angel Island, splits apart as the Sonic and the Death Egg land on the ground below, and voila, title screen.
 * The Lost Woods: Mushroom Hill Zone.
 * Manual Misprint: A few of the enemies from Sonic & Knuckles showed up in Sonic the Hedgehog 3's instruction manual.
 * Marathon Level: The stages, compared to previous games in the series, are exceptionally long, but both acts of Sandopolis Zone and Carnival Zone Act 2 definitely stand out.
 * Good luck finishing Death Egg Zone Act 2 (where your time at the end of the stage carries over to the final stage) in under 10 minutes.
 * Magikarp Power: While Sonic and Knuckles unlock their Super Mode after getting 7 emeralds, Tails doesn't unlock his until he collects all 14 emeralds. However, his Super Tails abilities--particularly the four birds who will attack any enemies or bosses in Tails' vicinity--are even more of a Game Breaker than Hyper Sonic or Hyper Knuckles in that you can literally kill almost every boss just by standing in one spot (since you're invincible) and letting the birds kill the boss for you.
 * Minus World: As Hyper Sonic, you can glitch-dash through walls into areas normally only accessible by Knuckles. A Pandora's Box of further glitches can be triggered from here.
 * The Missingno: Blue Knuckles, and his even glitchier Super Mode.
 * Mission Pack Sequel: Sonic & Knuckles to Sonic 3.
 * Mirror Boss: Knuckles if you play as Sonic and/or Tails, though he's ridiculously easy to beat. He is pretty much the same Knuckles you can play as, with the additions of a punch attack and the ability to block by ducking. He even takes Collision Damage, though trying to walk into him will just get you punched. But you can stand in front of him and get Tails to walk into him from behind if playing as Sonic and Tails. Tails takes damage too, but he's invincible (in 2P mode). If Knuckles drops from a glide on your head, only he'll take collision damage.
 * Mobile Factory: The Flying Battery Zone.
 * Mutually Exclusive Powerups: The three shields.
 * No-Holds-Barred Beatdown: Knuckles in Hidden Palace Zone.
 * No One Should Survive That: Par for the course with Dr. Robotnik. Upon being defeated in Lava Reef Zone, his craft is engulfed in lava (which instantly hardens).
 * Nostalgia Level: Hidden Palace Zone is a treat for those who had been wondering about that level that only existed as a song in the options menu of Sonic 2. The giant ceiling laser from Flying Battery Zone is clearly a reference to That One Boss from Sonic 2s Wing Fortress Zone. In Sky Sanctuary Zone, you fight a rehash of the wrecking-ball boss from Sonic 1s Green Hill Zone, and the boss with the spinning things from Sonic 2's Metropolis Zone.
 * Flying Battery's mid boss is also a Wing Fortress reference: A laser cannon that shoots giant beams of destruction while two pillars of light keep you trapped inside. The spiked platforms are conspicuously absent, though.
 * Marble Garden's mid-boss uses a burrowing attack based on Mystic Cave's boss.
 * One Game for the Price of Two
 * Ordinary Drowning Skills: Particularly funny in light of Death Egg Zone and Doomsday Zone, as noted above. Sonic can breathe in space, but he still drowns under water. Even Super Sonic can drown. Only Hyper Sonic has Super Not-Drowning Skills.
 * Oxygenated Underwater Bubbles: Present throughout Hydrocity, and can be released by bursting open underwater balloons in Carnival Night Act 2. There's also water in Angel Island, and Act 2 of both Icecap and Launch Base, but you have to use Debug Mode to access the bubble for those levels, as they aren't already placed.
 * Personal Space Invader: Mega Chopper in Hydrocity Zone.
 * Poison Mushroom: The powerup monitors with Robotnik's face on them.
 * Poor Communication Kills: Hidden Palace Zone has a mural showing Robotnik with the Master Emerald in his hands, and Super/Hyper Sonic confronting him. Knuckles misintepreted this as Robotnik trying to save the Master Emerald from Sonic, and thus treated Sonic and Tails as enemies!
 * Power Floats: Super Mecha Sonic. Both of Sonic's super forms also hover above the ground when they're at full speed.
 * Power-Up Letdown: Because there are no levels with water from Mushroom Hill onward, the Bubble Shield becomes this.
 * Puzzle Boss: Many.
 * Carnival Night Act 1: You hit the boss to make it expose its weak point, but the actual damage is done when the bouncing spike platform collides with it.
 * Flying Battery Act 1: You trick the boss into hitting itself.
 * Flying Battery Act 2: The mini-boss is a laser in the ceiling; you dodge it until it completely tears up the airship.
 * Sandopolis Act 1: You beat it by knocking it or luring it into a quicksand pit.
 * Lava Reef Act 2: You survive until Robotnik's own attacks destroy his machine.
 * Death Egg Act 2: You defeat the first boss by manipulating gravity to hit it with its own mini-bots.
 * You can also spin-dash at a minibot that has its spikes stuck in the floor/ceiling to catapult them at the boss.
 * Doomsday: You maneuver so the Robotnik-mecha's own missiles hit it in the face.
 * Quicksand Sucks: Sandopolis Zone, and Desert Palace Zone from the 2-player mode. Also, Marble Garden Zone featured tar-like stuff that behaved the same way as the other examples of quicksand.
 * Recurring Riff: The "Level Clear" music from this game has been reused by many other Sonic games, and even shows up as Sonic's victory music in Super Smash Bros. Brawl.
 * Sand Worm: Wormlike badniks in Sandopolis.
 * Secret Bonus: Complete an act with the clock on 9:59 (one second before a Time Over) and you are awarded 100,000 points, enough for two extra lives! Not easy as it is at that time you must land the critical hit on whatever boss you're fighting.
 * Easiest with Knuckles in Carnival Night Act 2, as he doesn't fight a boss. Just stand in front of the capsule until 9:58 or so and then jump and break the capsule. Requires patience.
 * Secret Level / True Final Boss: Doomsday Zone, which is only accessible if you beat Death Egg zone as Sonic, with a full set of emeralds, and is just an extended fight with Robotnik's final Egg-Mecha.
 * Also in the other levels, many nooks and crannies are only accessible if you're playing as the right character.
 * Segmented Serpent: Flying enemies in Angel Island, flying enemies in Mushroom Hill, sand worms in Sandopolis, and yet more flying enemies in Lava Reef. Hitting them anywhere besides the head will injure you.
 * Sentry Gun: A few can be seen in Lava Reef Zone.
 * Sequence Breaking: It's possible for Tails to skip a few midbosses simply by flying past the area where you fight them.
 * Shifting Sand Land: Sandopolis Zone. And Desert Palace from the 2-player mode.
 * Shout-Out: The final boss and mural seems to be taken from Nausicaa of the Valley of the Wind.
 * Slippy-Slidey Ice World: Ice Cap Zone.
 * Smart Bomb: When lightning shield meets water, Hyper Sonic does a double jump or Hyper Knuckles hits the wall.
 * Smashing Hallway Traps of Doom: Ice Cap Zone and Sandopolis Zone have the most of them.
 * Songs in the Key of Panic: In Doomsday Zone, the music speeds up if you're low on rings.
 * Spell My Name with an "S": So, is the Special Stage game you get when locking on Sonic & Knuckles with Sonic 1 called Blue Sphere or Blue Spheres?
 * Spiritual Successor: Flying Battery Zone to Wing Fortress Zone from Sonic 2. Carnival Night Zone would appear to be this to Casino Night Zone from the name, but besides being brash and colourful levels they don't share much in detail.
 * The Spiny: There are a few of them.
 * Stalactite Spite: The stalactites and icicles in Lava Reef Zone and Ice Cap Zone, respectively.
 * Stalked by the Bell: In Sandopolis Act 2, ghosts start to appear as lights in the level go out, and will start attacking unless the player continues to switch new lights on.
 * Story-Driven Invulnerability: At several points, Robotnik shows up outside of a boss fight but cannot be destroyed . The most notable instance is during his theft of the Master Emerald.
 * Super Not-Drowning Skills: Bestowed by a Bubble Shield. Fridge Logic dictates that gas exchange between the water and the giant air bubble would not be able to keep up with Sonic's respiration, so Sonic would still run out of air, but who cares?
 * The Hyper forms of Sonic and Knuckles can breathe underwater without the bubble shield, but by the time it becomes possible to get these forms, you've already passed the last level with water in it. Breathing underwater is thus only relevant if you're replaying any of the zones with water on a save file.
 * Super Mode: In addition to the usual Super Sonic, it's also possible to play as Super Knuckles. And if you collect all 14 Emeralds you can become Hyper Sonic, Hyper Knuckles, or Super Tails.
 * Temple of Doom: Marble Garden Zone, Hidden Palace Zone.
 * Temporary Platform: Some are present in various zones.
 * The Computer Is a Cheating Bastard: Inverted, in Hidden Palace Zone, Sonic can be airlifted by Tails to a hidden area where there are 30 extra rings. With those and the other rings that aren't hidden, Sonic can turn into Hyper/Super Sonic for the Knuckles battle.
 * Worse when Tails transforms, as any boss or enemy (except Knuckles) will get pecked to death by Tails's Super Flickies.
 * Without the 7 Chaos/Super Emeralds, however, Knuckles plays this straight; His spin jumps and spin dashes take priority over Sonic's, and he can block your spindashes by crouching. You can't block his. When he's attacking with a glide, however, you can hit him nearly anywhere that isn't his fists. Oh, and he can punch you in the face if you walk too close to him and he's not attacking you.
 * This Is a Drill: All of the bosses from Marble Garden Zone.
 * Some regular enemies also have drills.
 * Timed Mission: Every level has a time limit of 10 minutes. In the Doomsday Zone, your time limit is imposed by Sonic's Super Mode slowly draining the rings in his posession; run out of Super Mode and you fall to your death.
 * Used to great effect in Knuckles's version of Sky Sanctuary. Angel Island is slowly sinking in the background and will drop off the screen at the 10 minute mark.
 * Totally Radical: The monkey badnik in Angel Island Zone, an obvious update of the similar Coconuts badnik from Sonic 2, according to the manual glories in the name of Monkey Dude.
 * Underground Level: Endless Mine from 2-player mode.
 * Underwater Boss Battle: The Hydrocity Zone
 * Underwater Ruins: Hydrocity Zone again.
 * Unwinnable by Insanity: As seen in this series. There are many other ways to get stuck, but these in particular force you to lose all your lives or reset the game in order to continue playing.
 * Angel Island: [standalone Sonic 3 only] During Act 2, enter and exit a bonus stage or special stage to remove the boundary preventing Sonic from returning to Act 1. Once back in Act 1, stand on top of the left-pointing wall-spikes under the crumbling cliff, face left and look up. While the screen is scrolled up, have Tails air-lift Sonic until the spikes are just out of sight. Let Tails descend with Sonic in tow, and he will be hurt and fall into the wall. When Tails returns, have him lift Sonic up to just below the slope above. Hop off to the right and walk over an invisible floor under the slope; he will fall through an invisible shaft, and land in Knuckles' boss area. Start to play Knuckles' Act 2 as normal, hitting the checkpoint under the breakable floor. Unfortunately, the lower boundary is locked too high, and trying to progress causes Sonic to die as though he fell into a bottomless pit. When Sonic respawns at the last checkpoint, the breakable floor returns, and he cannot escape from Knuckles' Act 2. (In Sonic 3 & Knuckles, the offending checkpoint is removed.)
 * Marble Garden: In Act 1, as Hyper Sonic, find the only spinning top on a pedestal in the act. Head to the right, and drop into the area under the moving platforms, where the Lightning Shield is. Stand right next to the right wall, and crouch until the camera scrolls all the way down. Jump as high as you can; the game will bug out, and drop Sonic into an eerily empty version of Act 1. Go to the location of one of the Super Rings (it's the one that's normally at the end of a hidden tunnel to the right of a 1-up monitor). This will trigger the Act 2 boss fight(!). If Eggman is defeated, the timer stops and the Egg Capsule hovers down as usual, but the Capsule will be impossible to hit in this location. Since the clock has stopped, and the screen is locked in place, there is no way to lose a life. The only way out is to reset the console.
 * Carnival Night: In Act 2, as Hyper Sonic, crouch under the last set of spikes before the area where Knuckles shuts off the power, until the camera scrolls all the way down. Let Tails airlift Sonic into the spikes and fly all the way to the right, getting Sonic stuck in a wall. As Sonic, jump and hold left. This will allow them to bypass a checkpoint completely. After the cutscene with Knuckles plays, touch the checkpoint and enter the bonus stage. Upon returning, the lower boundary will be set much higher than normal, and the water will be missing. Jumping down into the normally flooded section will kill Sonic, as if he fell into a bottomless pit. Even after respawning, the lower boundary isn't set to the correct position; there is no way to complete the level.
 * Unwinnable By Mistake: When playing as Sonic with Tails tagging along, it's possible to glitch Tails off-screen so he doesn't return. Doing so in Marble Garden Zone makes it impossible to fight the boss.
 * Also, in the Sonic 3 only version of Hydrocity Zone Act 2, it's fairly easy to go past the boss and right to the capsule without doing the boss fight. But the only way out is to reset. The clock continues to run despite hitting the capsule, but unfortunately, even time over doesn't save you. The only way out is to reset and then it will usually let you go to Marble Garden.
 * Marble Garden [standalone Sonic 3 only]: When Sonic and Tails enter the Act 1 Boss room, stop just before the Tunnelbot is onscreen. Controlling 2P Tails, defeat the Tunnelbot just offscreen. Once the signpost falls, Act 2 begins to load; if Sonic is standing too far to the left, he'll be outside Act 2. The game will have no idea how to handle the situation, and effectively freeze. (In Sonic 3 & Knuckles, if Tunnelbot is defeated offscreen in this way, the camera will promptly scroll right, pushing Sonic within bounds of Act 2 before the signpost lands.)
 * Carnival Night: When Sonic is damaged while floating over anti-grav pads, he'll fall through. In some places, anti-grav pads are all that separate Sonic's Act 1 from Knuckles' Act 1. If Sonic accidentally falls into the first half of Knuckles' Act 1, and hits the first checkpoint, the only way to continue is to exploit a bug in Sonic's Super or Hyper transformation that allows him to pass through spinning barrels. If Sonic doesn't have all the Emeralds, doesn't have enough Rings to transform, screws up the exploit, or dies and respawns at that checkpoint, he's stuck.
 * Urban Legend of Zelda:
 * There tends to be confusion as to why the original Sonic the Hedgehog could not be locked in with Sonic & Knuckles. The two most popular explanations are Knuckles would have dramatically altered the color pallet or that Knuckles gliding on conveyor belts in Scrap Brain Zone would cause the game to crash--both of which were debunked by the famous rom hack "Knuckles in Sonic the Hedgehog 1."
 * Video Game Caring Potential: Many players have commented that they did not have the heart to leave the injured  on his own in Sky Sanctuary Zone.
 * Walk, Don't Swim: Tails can swim. Knuckles can glide in the water. Sonic sinks like a rock.
 * Walking on Water: You can run across the surface in Hydrocity.
 * Wasted Song: Some of the music from the individual Sonic 3 gets Dummied Out if you're playing the two games in tandem, including the fantastic miniboss music.
 * It's interesting to note that if you are playing Sonic 3 by itself and gain invincibility during the mid-boss of Hydrocity Zone, the song will switch to the Sonic & Knuckles mid-boss music once the invincibility wears off. The tune otherwise doesn't appear in Sonic 3 at all.
 * Weaksauce Weakness: Fire shields let you run over molten magma and lightning shields make you a ring magnet and immune to electricity, but both are immediately cancelled if you touch water. Annoying in the Sonic 3 portion, with water in 5 of its 6 zones, but not once you reach the Sonic & Knuckles levels which have no water sections at all.
 * Weaponized Exhaust: If the boss uses a rocket to fly, it can use that rocket to hurt you. Luckily, though, The Dev Team Thinks of Everything; if you have a fire shield, you're unaffected by the exhaust, giving you a great angle to attack from.
 * Weather Control Machine: Featured in Mushroom Hill Act 2.
 * Wrap Around: A few areas in Ice Cap Zone and Sandopolis Zone tend to loop when not exited from them properly. With the Hyper Sonic in Sonic 3 cheat, you can wrap around back to the first act of a zone, resulting in messed-up graphics and other glitches.
 * X-Ray Sparks: When Knuckles gets electrified.