Lowered Monster Difficulty

A form of Villain Decay. The longer a monster is seen on screen, the easier it gets to defeat or avoid. Maybe mowing down the cannon fodder tired it out or something. If a writer is good, they'll have some damage occur to it from previous battles, or deliberately point out that the monster is toying with the main characters more due to personal grudge. Otherwise, it's clearly the plot giving the main characters a break.

This is especially obvious when the heroes don't have any powers or anything technically to distinguish them from any of the other humans that were easily killed.

Aspects of Lowered Monster Difficulty include:
 * You can see it coming. Early in the movie or show, the monster hides in the shadows, and kills its prey without even being seen. It can also be anywhere it wants to be as long as nobody was looking at it. Now it can be detected from a distance, and moves a lot slower. The heroine can outrun it long enough for an escape plan.
 * It takes its time to kill the main characters. Non-important characters like police officers are killed in seconds. For the main characters, it just stands there and roars, or makes threats or evil jokes, and even when it attacks, it tends to miss a lot. The villainous equivalent to Kill Him Already.
 * Attacks that previously did absolutely nothing start actually affecting it. Gunshots start knocking it back, and punches and kicks may cause it to recoil.
 * Newfound respect for Mook Chivalry. If the menace is a pack of creatures whose teamwork was what let them prevail over the victims, they may suddenly decide to engage the main characters one by one and get taken apart piecemeal.

If the monster becomes less difficult when there are many of them, that's Conservation of Ninjutsu - of course, contrast with the fourth clause above. Related: Strong As They Need to Be, where the heroes' powers fluctuate as the plot demands.

In video games, this may downgrade bosses into regular encounters. If the monster's difficulty decreases over a long series, it may be because the characters are getting stronger and the monster can't catch up. In role-playing games, however, this is to be expected because in most cases, your party gets stronger while the enemy monsters don't.

Compare Sorting Algorithm of Evil, Third-Act Stupidity, Why Don't Ya Just Shoot Him, Villain Decay.

Contrast Team Rocket Wins.

Anime and Manga

 * In Black Lagoon, Lowered Monster Difficulty is the only reason Revy was able to hold her own against Ninja Maid Roberta in a fist fight. Otherwise she wouldn't be standing for very long.
 * Considering that after the fight was over Roberta just needed a little help up and Revy was out cold for hours, it wasn't really that impressive of a "hold her own".
 * Hansel and Gretel are a better example: after showing both skill and deviousness when fighting a bunch of Mooks one of them and the other.
 * There is a explanation for both, though;
 * This is very prominent in Bleach, where the main character Ichigo goes from barely being able to beat simply Hollows, to defeating a squad captain in less than one year.
 * Another example is that of Uryuu Ishida, who can in the beginning of the story kill one Hollow with one arrow, and later on gains a new type of bow which allows him to fire one thousand and one arrows per second, allowing him to kill hordes of Hollows in mere seconds.
 * Also seen with the Boomers in Bubblegum Crisis. Curiously, their armor also seemed to get weaker as attacks that merely bounced off early on do more and more damage the longer they are on camera.
 * Major 'boss' fights in the Claymore anime take several episodes to defeat, and as a result the weakening of each boss fits every bullet point of this trope to a tee. Even the obligatory constant taunting.
 * Perhaps justified, in that they usually use superior numbers and delaying tactics to prolong the battles and wear the opponent out. In effect, they're invoking this trope.
 * In Fate/Stay Night the anime, Saber and Shirou's battles against Gilgamesh and Berserker -- the two strongest opponents they face in the series are also examples of monster weakening. In the beginning they are no match for their opponents, but in a rematch and after fighting for so long, the enemies attacks seem less effective, and their defenses are penetrated easier. To be fair, the heroes do improvise ways to overcome their enemies, but they are still inexplicably able to withstand more punishment than they could the first time.
 * Especially odd in Gilgamesh's case. Canonically, he is the single most powerful Servant, PERIOD. It's generally agreed that, while not the most powerful character in the Nasuverse (Zelretch and Archetype Earth can probably beat him), against any other Servant there is no reason he should ever lose. The only reason Enuma Elish is survivable at all is because he's deliberately holding back its full strength. The guy is deliberately lowering his own difficulty, mainly due to his galactic-sized ego. If he was a bit less arrogant and a bit more of a Combat Pragmatist, he'd wipe the floor with everyone.
 * However, he could potentially destroy himself if he used more power, Ea being an Anti-World Noble Phantasm and all.
 * Occurs in season 2 of Mobile Suit Gundam 00 to an extent with the, whereas in the first season, a force of a few dozen of them plus support from   and luck managed to  , in the second season they become nothing more than elite mooks,
 * Bakemon grew much weaker over the course of Digimon Adventure. When they first appeared, it took two Champion-level digimon and some assistance from Jyou to take on a single Bakemon. (Okay, so that was kind of a Giant Mook, but the regular-sized Bakemon still were rather competent.) When they return as part of Phantomon's army in the Myotismon saga, they still require the chanting in order to be weakened, although this could be attributed to power in sheer numbers--maybe. But by the time Myotismon is defeated (right before coming back as VenomMyotismon), they are apparently so weak that the Digidestined's Digimon can each take out multiple Bakemon single-handedly at their rookie stage.
 * This could have less to do with the Bakemon being weaker, and more to do with the Digidestined's Digimon becoming stronger.
 * Even worse is the Sailor Moon R movie. At the beginning, all five characters are barely able to take down one flower creature. Shortly afterwards, they are taking down the exact same enemies in crowds. Each.
 * Justified, the first creature was mature, and upgraded (on camera, no less) with the life energy of a few dozen people. The field was composed of immature buds, and didn't siphon any souls.
 * Subverted in Tengen Toppa Gurren Lagann, when the enemies However, shortly after this,.
 * The mechas used in Utawarerumono were at first very destructive and nigh invincible. Later they are defeated so easily that they are brought down off screen. They didn't even bother showing how they were taken down. Hakuoro destroys one with a single stroke.
 * Somewhat justifiable; by this point,
 * Done intentionally in Street Fighter II: The Animated Movie. Bison, who is virtually omnipotent, decides to fight Ryu and Ken as a straight martial artist by not using his Psycho Power.
 * In Kikaider, he fights a new Monster of the Week. Fighting one alone is usually no easy task for him, but in the OVA series, Gill is creating an entire army of duplicated copies of all the robots he ever fought. He managed to kill all of them, with lightening speed. Though this isn't to show the monsters got weaker as much as Jiro became an unstoppable killing machine.

Films -- Live-Action

 * A few of the monsters from the Godzilla series suffer from this (notably King Ghidorah), but none worse than Hedorah. In Godzilla vs. the Smog Monster, he's arguably Godzilla's most powerful foe in the entire original series (with the possible exception of Mechagodzilla). Decades later, in Godzilla: Final Wars, he's killed in about 20 seconds.
 * In the second Alien vs. Predator film, the Aliens are severely weakened. While the other films (include the first Alien vs. Predator) tended to vary exactly how powerful they were and the precise nature of their abilities, this one kneecapped them almost entirely for the sake of the Predator protagonist.
 * Ip Man shows the fourth clause in his fight against ten Japanese pugilists. Immediately before that, in Master Liu's  3v1 fight, the Japanese pugilists were clearly working together to prevent him from comboing any of their number down. However, when the titular hero goes to bat, none of them interfere when he pulls off his Rapid-Fire Fisticuffs Finishing Move on any of them. It would perhaps have made the fight more "realistic" to have them interrupt. It would also have further increased Ip Man's Badass quotient if he had done Jason Bourne-style Offhand Backhand "wait your turn" strikes to stop interlopers. Although it may be a Justified Trope if you believe that martial artists can sense intent, as Ip Man's being on a Tranquil Fury Roaring Rampage of Revenge would have given him enough violent intent to make his opponents hesitant about bumrushing him.
 * One of the most jarring cases of this occurs in Jurassic Park 2. Dinosaurs who are ruthlessly efficient and accurate when taking down most of their victims do mind-baffling stupid things when facing the lone woman and little girl in the area such as patiently waiting for the little girl to finish her gymnastics routine which ends with the Raptor kicked away somehow, despite how small she is and how little momentum she had accumulated or fighting amongst each other for the 'right'(?) to kill the fleeing woman.
 * The raptors also suffer badly from this in the first Jurassic Park movie as well.
 * By contrast, the Raptors in the novels remain dangerous over both books, even when they're not directly threatening the protagonists. The T-Rex actually becomes more dangerous in the second novel, when
 * The Matrix movies are a pretty good example of this. In the first film, one of the things that makes Neo special is that he's on par with the Agents. In the second film, he even ACKNOWLEDGES that the Agents have had "upgrades"... but the rest of the cast can hold their own against them, most notably in Morpheus's truck top fight.
 * Niobe and Ghost outright kill several Agents in the canonical Enter the Matrix game. They could still possess someone else; but still so much for "nobody has ever beaten one."
 * The "upgrades" are increased speed and strength in exchange for reduced intelligence. That makes them better against Neo (if only barely), but less effective against everyone else.
 * This can be explained away though simply by Neo's presence. Considering that the Matrix is a "You are as strong as you think you are" kind of place, but everyone knows they are weaker than Agents. Then Neo comes along and everyone knows, subconciously, that a human *can* beat them.
 * To an extent, the Kraken in the second Pirates of the Caribbean movie. In its first appearance, it snaps a (small) ship with its mighty tentacles while dragging it down in instant. In the subsequent appearances, menacing the heroes, its tentacles slowly curl around the (significantly larger) ships. Since Will Turner had been subject to an attack on the Kraken's second victim, he was able to quickly devise a plan to temporarily counter it. Perhaps because they couldn't find a way to have the heroes kill it without it being an even worse cause, in At World's End
 * The critters in Pitch Black are a prime example of this trope. At the beginning of the film, they are clearly crawling around while there's still sunlight visible. Later on, a dimly luminescent glass jar can send them screaming away.
 * Roger Ebert called this the "Hero's Death Battle Exemption" and cited the movie Prophecy as an example. In this movie, a killer bear shredded normal humans in seconds, but was considerate enough to let the hero stab it in the head multiple times with an arrow, which took ten times longer than it had killed anyone previously.
 * The Arachnids in the film Starship Troopers are classic examples of the trope: in the first major battle scene it takes a fire team of soldiers blasting away on full auto to put down one. In the final battle scene, a trio of heroes with the exact same weapons mow them down by the dozens, and other soldier do so as well. Arguably justified -- Within the movie there is a newsreel, by Neil Patrick Harris no less, explaining that you need to aim for the nerve stem to bring down an Arachnid warrior. Shooting off a single limb still leaves the Arachnids 80% combat effective. In the first battle scene, all the troopers are just mindless shooting off limbs, but later on you can see them aiming for the nerve stems. The main characters are veterans of a few battles, and are more experienced.
 * Averted in Tremors. The first few victims were killed and sucked through the ground without giving them a chance to escape. By the middle of the film, we had two of of them going after a single person, and even one coming up directly under her and she still managed to escape. By contrast, a few Graboids learn and plan, and all refuges become either temporary or a second form of slow death as they work out how to get their prey.


 * Justified in the first Terminator movie; it made sense that the Terminator was getting weaker by the end, due to all the damage it has slowly been accumulating throughout the movie. The suspense lay in the fact that the heroes had been getting hurt and killed too.
 * Same thing goes for the T-1000 in the 2nd movie, although because of its regenerative abilities, it isn't as apparent in the theatrical film. In some of the extended scenes at the end, however, the T-1000 starts "glitching" - his hands and feet mimicking and melting into the surrounding environment. It seems that getting frozen by liquid nitrogen, heated up by molten steel, and then attempting to reform without any mistakes would mess anyone up.
 * The T-800 is so durable that in the first three movies it takes an entire movie to destroy one (and the latter two were suicides), but in Salvation John Connor destroys one in only a couple of minutes.
 * That was actually a T-600.
 * The only reason Indian Joe from the Tom and Huck movie with Jonathan Taylor Thomas doesn't come out on top is he acts like a spider: He surveys his prey, walking s l o w l y toward them, and if they run away, he follows at a leisurely pace. Even when he's trying to take revenge at the end, even when he momentarily catches Tom (who pulls free and runs off). This, despite the fact that he's been shown to vanish in a split-second when he confronts Tom halfway through the movie (so obviously he moves fast). He lost only to a sort of very odd hubris.
 * The Demon in Wes Craven's New Nightmare.
 * In A Lonely Place To Die the bad guys range from being crack shots with their rifles to being hopeless marksman depending on who they are shooting at; they are hopelessly unable to hit the fairly nearby heroine as she slowly climbs away from them in broad daylight but a few hours later one of the same gunman can effortlessly hit someone (twice!) through a window at night with fireworks going off around him.

Literature

 * The eromakadi (eaters of light) from The Journeys of the Catechist. At the beginning they are nigh invincible spirits sucking good things out of the world, the main characters attempt to escape them then barely manage to take out one. In the third book the main character effortlessly dispatches two then weaponizes their bodies.
 * The monster in any James Byron Huggins novel. In the first act, the genetically-engineered super-dragon will be destroying tanks and if it escapes it could destroy cities, while the third act it can be killed by some strongman with a viking axe and a couple of grenades. Same thing in Hunter; the monster rips apart heavily fortified labs and squads of armed guards only to die from being lit on fire in single combat with the hero.
 * The more Denarians you see in The Dresden Files, the easier they get to kill. The first one took three Knights of the Cross to take down. By the time we see three more, the Denarian leader versus one Knight is pretty even. More than a dozen pop up, and they're not much more than ordinary mooks. Partially justified, as the dozen were picked for desire rather than skill, but the drop in capability is still pretty drastic.
 * Also partially justified in that Harry tends to take at least one level in badass each book, and tends to soup up his magical arsenal in the downtime between books.

Live-Action TV

 * The Ubervamps in season 7 of Buffy the Vampire Slayer. Took Buffy SEVERAL EPISODES to kill ONE of them... and in the finale, each of the newbie slayers takes down dozens.
 * And even that one Ubervamp had lowered difficulty, going from stake-deflecting skin to being decapitated with wire. (Buffy's hands presumably got an upgrade to avoid having her fingers cut off in the attempt.)
 * Not only Slayers, but normal humans Giles and Wood (badass normals), Dawn (sort of a badass normal), Xander (sort of a badass normal just due to years of experience), and Andrew and Anya (just normals, not badass at all) are able to dispatch some of them, sometimes without even hitting anywhere near the heart.
 * Writer/creator Joss Whedon even mentioned this in the episode's commentary, handwaving the problem by saying that that "isn't what it's about."
 * Normal vampires had similarly varying levels of capability. It would seem more likely the "ubervamps" weren't really any better than the earthly variety, just uglier. The first one was probably handpicked by the first so it was very hard -- like the vampire Big Bads in the early seasons -- while the rest were just common Mooks.
 * Daleks, from Doctor Who, tend to suffer from a strange form of this. Depending on the writer, episode and situation, the Dalek can be a godlike mass-murdering killmachine immune to bullets, missiles and everything else - or capable of being defeated by having their eyestalk covered with a hat.
 * The new series tries to have it both ways. In keeping with its new action-dramedy look, it goes the godlike, mass-murdering killmachine route with the Daleks, even trying to make their truly ridiculous design look threatening. And of course, the thing about the Daleks is that there is only one thing they ever do with other species: "Exterminate!" Despite this, every Dalek two-parter in the new series has relied on the Daleks having the Doctor, his companions, and other important characters at their mercy halfway through the story, gearing up to "Exterminate!" the hell out of them, and then deciding "Maybe later." At one point, they put it off for no apparent reason other than plot necessity.
 * In the Doctor Who episode Blink, the enemies can move so quickly that if you so much as blink, they'll rush forward and drag you decades into the past, but they will turn to stone as long as you're looking at them. Apparently, they lost their exceptional speed halfway through the episode, conveniently before the central characters arrive for the final scene.
 * In what is a rather brilliant way to mess with the fourth wall, the audience is what saves their lives. Whenever the characters turn around, the angels only ever move just close enough to not get into the cameras field of view. It's also more apparent when the characters are inside the Tardis and the camera is outside of it, the angels can still only move when the lights go out because they revert to statues when the camera sees them. This is also the way the angels could have beaten the Doctor, because it all happened before the cameramen got there.
 * The Cybermen acquired a large collection of weaknesses during the run of the original series, but the treatment of their aversion to gold amounts to Serial Lowered Monster Difficulty. In the Tom Baker story "Revenge of the Cybermen," gold was described as the perfect non-corrosive metal that killed by plating the Cyber breathing apparatus. Gold dust was the key, and man had invented he glitter gun. By "Earthshock," the Davison Doctor was able to scratch open a Cyberman's chest plate using the point of Adric's gold star. Then in "Silver Nemesis," even round gold coins were enough to do the trick when used as arrowheads.
 * The mysterious Monster on Lost is portrayed in the first season as a deadly killing machine that strikes fear in the heart of the survivors. After it is seen onscreen for the first time in the second season, however, everything goes downhill as the survivors no longer fear it to the same extent they once did. Culminates in the fourth season when the Monster attacks a group of redshirt mercenaries but only kills one of them, despite the mercenaries' weapons being shown to have no effect on the Monster, which begs the question of how they managed to survive its attack.
 * The motives of the monster are something one should really not discuss. It could have easily wiped out all of the mercenaries but since it did not it knows why. It's not like killing mercenaries is it's job.
 * The Mooks in Power Rangers are subject to this, sometimes painfully so. For example, in the first episode of S.P.D., a "Bluehead" ("Orangeheads" are a different story), or leader of several standard-issue mooks, is cause for alarm. As the series goes on, they slip further and further down the ladder, until the season finale has the Rangers fighting off swarms of them, bare-handed and unmorphed.
 * Not even the monsters of the week are immune to this. Take for example whenever a large group of monsters are sent to deal with the Rangers in Mighty Morphin' Power Rangers, they'll usually be defeated in no time flat, and are often nerfed to the point where they lack their original abilities and just use physical combat to fight the Rangers.
 * The titular monster in SS Doomtrooper is a mutated Nazi Super Soldier that, after proving completely Immune to Bullets and capable of ripping entire battalions of soldiers into pieces, is finally killed in a one-on-one fight with the main character, who cuts off its arm with a knife.
 * Stargate SG-1: Jaffa armor could initially withstand automatic weapons fire for a decent amount of time before a bullet got through. As the series wears on, Jaffa armor resilience decreases, eventually reaching the point where they may as well be wearing nothing. This may be explained by a switch to more appropriate ammunition.
 * A straight example is the Goa'uld. In the first season, they are nearly Immune to Bullets, requiring A LOT of firepower to take down permanently, and have super-strength. On multiple occasions, a single Goa'uld is capable of giving the SGC a run for its money. By the 2nd season, they are as harmless as any human if you can get them away from that shield generator of theirs.
 * Stargate Atlantis has the Wraith. In early episodes, killing or even disabling a Wraith is insanely difficult. Later on, Wraiths become almost as easy to take out as humans. Unlike the Jaffa, no reason is given for this. During their first appearances, killing a Wraith requires emptying an entire magazine from a P90 and a some luck. By season 2, Wraiths die not only from a single burst from a P90, but are as easily killed by a few bullets from a 9mm pistol or a single stab from a knife.
 * Later it was explained that the Wraith were losing their food source and that almost works until they start wasting their energy reviving people.
 * The Borg of Star Trek also had some of this. After adapting to the Enterprise's weapons in their first encounter, a Borg Cube is initially completely impervious to all attacks by Federation ships, able to single-handedly destroy a fleet of 39 ships while taking no significant damage in return and is only stopped in the end by Hollywood Hacking the hive mind. Later depictions have toned down this perfect adaptation, such that in Star Trek First Contact, a large fleet of ships is capable of damaging a Cube and eventually destroying it by aiming at a weak point.
 * Actually, during the first time they were immune to Federation attacks because they had just assimilated Picard, who knew all about Federation weapons, technology and tactics. By the time of First Contact, it stands to reason that the Federation had developed new weapons (and possibly tactics) specifically to fight the Borg, which Picard obviously couldn't know about during his assimilation a few years earlier.
 * On the other hand the Voyager series finale averts this. Voyager could only defeat the Cubes because . Even then, the Borg adapt fast enough that the last Sphere is able to damage Voyager.
 * In the Star Trek the Original Series episode "The Devil in the Dark", the mysterious monster kills everyone instantly on contact, so no one has ever lived to see it, including many (presumably) armed. But when Kirk encounters it, he has time to agonize over the morality of killing it, and it stays away because of his weapon.
 * Justified: Until the Enterprise arrives, no weapon has worked against it; in fact Spock even has to modify the Starfleet phasers to make them more effective. The first time Kirk meets the creature, he shoots instantly, and severely wounds it; thus, on their next encounter, the creature has learned to fear his weapon.
 * Supernatural has moments like this in some episodes. The Wendigo in the same-titled episode is show to be a lightning fast, shadowy death machine and an expert hunter. Yet when the main characters confront it in its lair it just lumbers along casually despite the fact it knows they have weapons that can hurt it. It's not really surprising when it dies in one shot.

Tabletop Games
"If the foe is a super-strong monster that could kill or maim the hero with a single blow, it rarely strikes to inflict damage directly. Instead it slams the hero, or grabs him and tosses him around!"
 * GURPS has an optional cinematic rule for this.

Videogames

 * Yellow Squadron from Ace Combat 4. The first time they appear, they have Story-Driven Invulnerability and can't be hurt (although their AI is nerfed to prevent them from killing you if you run, which is your mission objective once they appear; they're no better shots than regular enemy jets). The game even warns you against trying to struggle against them by instructing you to turn tail and flee ASAP. The second time, even a dead hit only succeeds in annoying them into leaving. The third time, Mobius One does down one of them, but Worf Had the Flu. In subsequent encounters, though, Yellow Squadron planes do get shot down honestly to the last, including their best pilot Yellow 13 in the penultimate mission. In the very last mission, the Yellow Squadron pilots are pretenders to the name who lack the skills of the original, thus getting defeated more easily despite their superior numbers.
 * Also applies to Stonehenge from the same game. The first time it shows up as an obstacle, it's at the end of a mission where you probably were expecting a simple Mission Accomplished, you're forced to terrain mask by dropping into a naturally confined ravine, the One-Hit Kill shots come rather frequently and SkyEye can only predict the next round to less than 10 seconds, forcing you to stay inside the ravine. The second time, you are told in advance to expect it, the shots aren't as frequent so allowing you to actually do some useful bombing or dogfighting, SkyEye can predict the shots with enough advance warning and there are nice wide open plains to drop below 2000 feet with. The final time, the instakill shots only occur at the start and once you get in its face, it's all but a nonissue even above 2000 feet.
 * Unless of course, you fly in front of its barrel when it fires...
 * Alien vs. Predator
 * Played straight in the Monolith FPS with the Aliens.
 * Averted in the Rebellion FPS games, where the Aliens are highly threatening and tricky.
 * Igor, the second boss in Cave Story reappears right before the final boss. The interesting part is that he has the same amount of health and does the same amount of damage, and is indeed exactly the same as when you met him earlier. The only difference is that you have bigger guns.
 * Chrono Trigger has an interesting example. The plot requires you to fight the Final Boss at one point before the end, and he's even more difficult than he is then, not just because you haven't had time to grind levels or find the Infinity+1 Sword, but because he has many more HP and uses his ultimate attack almost immediately. Beating him then is one of two ways to get the developer's room ending, but it isn't practical unless you're using a New Game+. (The other way to get the ending is to choose to fight him as soon as the game starts, an option only available in a New Game+; if you do so, he's only as strong as he is at the end of the game, so beating him in the Hopeless Boss Fight is definitely worth some bragging rights.)
 * Mendoza in Command and Conquer: Renegade. He appears twice in the game before a climactic battle, only to be hurt a little and escape (even saying "I'll finish you later!" before flying off in a helicopter). He's invincible while escaping, and each time he returns, he's back to full health. When he finally fights a pitched battle against Havoc, he's at full health again, but as easily hurt as before.
 * Crysis has a fairly glaring example in the large alien robots called Scouts. Throughout the early part of the game they're shown as exceedingly deadly with one of them effectively killing off the players entire team (who all have his weapons and powers) with barely any chance for them to fight back. However when they eventually come after the player all three parts of the trope come into play they attack from plain sight forgoing the previous brutal ambushes they used, they don't simply grab and maul him in seconds like they did all his teammates, and simple machine gun bullets can suddenly kill them rather easily. By the end of the game the player is battling them in packs of up to a dozen with no real explanation for their sudden decrease in deadliness.
 * Also, in Crysis it's a major plot point that the largest alien war-machines (referred to as Exosuits in-game and as Hunters in the game files) have an energy shield that makes them indestructible and thus capable of single-handedly wiping out a few platoons of U.S. troops. However, in Crysis: Warhead, those same Exosuits somehow lack their signature energy shields, and you fight and destroy a few of them as "boss battles" throughout the game. Even the North Korean nanosuit soldiers are seen destroying an alien Exosuit.
 * In Dead Space the final boss, the Hivemind, suffers from this, as well as Anticlimax Boss. In a cutscene it instantly kills someone with a brutal horizontal sweep of one of it's giant tentacles. Despite the fact that this tactic would be equally effective against you, the Hivemind inexplicably only attacks with slow, highly telegraphed 'vertical' tentacle strikes that are easily dodged, and every couple of attacks it obligingly opens it's mouth so you can shoot it's weakpoints.
 * In Final Fantasy VI, it is possible at certain points in the game to bump into the Guardian, which is an invulnerable boss. The only way to survive the encounter was to run from the battle. The Guardian then reappears in the final dungeon, with the Guardian switching to "Attack Mode" when you face it as a proper boss. Before that it was in the unbreakable "Defense Mode".
 * Also inverted with Kefka, who turns from a comic relief pest who's Not Worth Killing when you first meet him, a wuss on the second encounter, a fairly difficult boss battle the third time, to curbstomping the Empire's finest warrior without even caring. And this is all before his ascension to godhood.
 * In Final Fantasy VIII you can recruit a Tonberry that can inflict this trope on monsters.
 * Videogame bosses are frequent victims of this: they can be damaged in the designated battle, but are invincible if the player encounters them before then. Two examples from the Megaman Battle Network series are Bass in the third game and ShadeMan in the fourth.
 * Ridley in Super Metroid subverts this. You briefly encounter him at the start of the game, and usually he'll end up reducing you to 20 energy before flying off. However, it's possible to deal him enough damage to cause him to flee.
 * Metal Gear RAY comes pre-decayed for your convenience. When introduced, they're introduced as a weapon built to destroy Metal Gear REX and its knockoffs. But Raiden can take out hordes of them more easily than Solid Snake could take out one REX.
 * There's an Ass Pull that
 * Fans wave this issue away, the Ray line is mass-produced, the REX line is custom made. In Metal Gear Solid, Snake can barely take one REX down. How many RA Ys does Raiden fuck up in MGS2?
 * Also, the REX was built like a tank. If it's attacked, it had the armor to simply absorb the attack. RAY was make to run or jump out of the way of the attack entirely, so it had light armor to reduce weight. Not that hard to imagine, since REX's attacks are so slow you can dodge them on foot. Explains the MGS2 fight, though it doesn't explain the MGS4 version.
 * The Boss in MGS3 is invincible in cutscenes. Every time Snake encounters her, his shoulder gets dislocated and his elbows get snapped. He is no match for her. Until you actually face her in a gameplay encounter at the end. Then she is defeatable and nowhere near as badass as she is in the cutscenes.
 * Justified in that up until then, Snake hadn't yet found the resolve to go all-out against her, as seen by him hesitating briefly during the encounters.
 * Actually, Snake does fare a little better each time he faces her. Compare his cut scene battle at the end of the game, where he actually keeps up with her for a while, with his battle at the start, where she completely destroys him.
 * The SA-X in Metroid Fusion undergoes one of these. Early in the game, it is introduced as a sort of Badass that you must run away from very quickly and will liquefy you if you look at it too long, but eventually Samus winds up defeating the SA-X. Can be justified, as Samus is slowly regaining her powers throughout the game. Plus, it's still not easy: in a straight firefight, Samus would get wiped out by the SA-X.
 * In Paper Mario, the recurring enemy Jr. Troopa has reduced HP resulting from having swum to Yoshi's Island and back in pursuit of Mario. This is somewhat mitigated by the addition of a spiked cap. Upon defeat, he then talks as though flight would have made the trip effortless.
 * Of course, Jr. Troopa's entire schtick is that he's a one man Terrible Trio, being substantially weaker than the heroes every time they encounter him. He's a tough fight, but it's difficult to lose to him.
 * The Necrons of Warhammer 40000 demonstrate this trope on a race-wide scale: at first, they were enigmatic and virtually unknown, and also virtually unstoppable. Fast-forward a bit to when they're a known presence in the galaxy by everyone with much less mystery, and they're bordering on Chew Toy status.
 * The last version of the game does not directly nerf them, but various rule changes hurt them so badly they are almost a joke now.
 * An entirely different type of of "lowered monster difficulty" is in R&D games like X-COM; you gain new technology that outclasses even the Big Bad aliens. This isn't can't catch up as the examples there do not match the case: Your entire team gets better; none of your characters gets left behind. The enemies get more powerful by normal Sorting Algorithm of Evil, but your team gets more powerful faster.
 * The Brutes in Halo. In Halo 2 they had no shields, yet could shrug off tons of damage and attempting to melee them was pretty much suicide. In Halo 3 they have shields, yet once those are gone they are pretty weak (outside of Elite Mook versions) and they can be beat around in melee combat. In Reach they rarely have shields yet aren't much tougher than unshielded Halo 3 Brutes (and can be beat around just as easily), and even the Elite Mook versions go down in a few headshots (bar the few that do have shields). This also coincides with them having less influence on the plot; they start off very important but by Reach they are just another type of Mook.
 * In Final Fantasy Tactics Advance, one of the main antagonists, Llednar Twem, has a law that makes him literally unbeatable (the in-game rules made it illegal to beat him, the actual gameplay simply made him invulnerable), there's a point in the game where a battle is won by surviving against him enough time. You actually watch as a judge nullifies this law and thus allows you to beat him.
 * .hack GU has this with Tri-Edge . He is invincible in the cutscene and effortlessly defeats level 133 "Terror of Death" Haseo, yet by the end of the game, you beat him while you are nowhere near your former glory. Of course, having teammates and healing potions probably helped.
 * Done in Monster Hunter Tri with the Deviljho. As soon as you hit rank 31 and the High Rank quests become available, you start fighting the monsters from the bottom of the pecking order: Great Jaggi, Qurupeco, and Royal Ludroth. Except that in any high-rank quest, there's the possibility that Deviljho will appear, which you're nominally not qualified to fight until rank 51. Thus when you initially encounter Deviljho, you have to run like hell if you want to live, and hope that either Jho or the monster you're tracking retreats from the room, but then you have to take down Jho like any other later on.
 * The Black Knight in Agarest Senki is a blunt example. You faces him three times. The first where he has a full HP rocovery ability and chain more than 4 comboes, killing you in one attack. In the second time, he's still tough because of his HP recovery, but he can no longer kill anyone in one hit if you don't play on hard. In the third time, you must beat him to clear chapter 1, and he isn't even that tough if you upgrade and fight properly.

Webcomics
"Emonika: Why are Uber Guilds so desperate to get into the Lower Mantle before anyone else? After all, there are plenty of other dungeons in game.
 * The webcomic The Noob hung a lampshade on it in episode 299: The comic's featured generic fantasy MMORPG "Clichequest" suffers not merely from a Lowered Monster Difficulty but from a Lowered Dungeon Difficulty as Dungeons and quests related to them "decay" over time.

Sir Bob: Emonika, you don't understand! ...Ah, to drink the first sip from the sweet chalice of success! To be cross-server famous! Ah, to be inspected by the awestruck crowds as you /dance the night away on the bank roof in your legendary gear! ...Like when I got this splendid hat on the third level of Tedious! It took weeks to plan.

Emonika: Pfft! I'm not even level 20 and I've been there three times already!

Sir Bob: That's because with every patch they make old content easier so that more people can do it. See, when a Dungeon is new it's almost impossible even to get past the entrance. Only the top elite guilds make progress at this state.... Nobody knows what lies ahead... Next, things get easier - And it's the turn of the casual guilds, i.e. people who raid very occasionally, like four times a week or so. Then, in time, the Dungeon is nerfed so much that it's completely abandoned, except for a few stragglers - newbies, gold farmers, people who got lost..."

Western Animation

 * Something of an inversion on this occurred in the Saturday morning cartoon of Dungeons and Dragons. In the first couple of episodes, the band of teenage/preteen adventurers are battling no less than Venger and Tiamat on a regular basis. Midway through the series they're having trouble with orcs and bullywugs. Near the end of the show's run, they had an episode where, in the process of helping some fairy-sized dragons escape to their homeland, they're overpowered and captured by a perfectly normal, two-bit human baron and his dozen or so men at arms....
 * Done at times in Teen Titans, perhaps most obviously in the episode "Revolution". At first Mad Mod's robot guards are so powerful that the Titans can't even defeat 2 or 3 of them- they're simply too tough. When they wind up fighting an entire army at once all of a sudden the Titans can rip them apart like tissue paper or knock them over like skittles.
 * That might also count as Conservation of Ninjutsu.