History Main / IncreasinglyLethalEnemy

** Blaziken is banned from competitive play for good reason. One of its abilities, Speed Boost, causes the Pokémon to gain one stage of a Speed buff at the end of every turn, which means it only takes about a turn or two to outspeed almost any Pokémon in the game.
** The ability "Moody" is even more broken than Speed Boost. At the end of each turn, it randomly raises one stat by ''two levels'', while another one is randomly decreased by one level. It can also raise/lower accuracy or evasion, and if evasion gets raised it essentially works as free Double Team, so good luck hitting a monster that on average gets stronger each turn. This ability made ''[[ComMons Bidoof]]'' completely broken, therefore it is no surprise it got banned in competitive play as well.

* ''Junkworld'' has enemies called Weirdeer, mutated stags with moderately high HP and low attack which will attempt to mutate further after losing half their health. If they don't die before they finish mutating, they turn into Voo-deer, two-headed humanoid deer monstrosities that have ''far'' more health and attacking power.

* The ''Anime/RanmaOneHalf'' fan fiction ''[[https://jusenkyo.fandom.com/wiki/Relentless Relentless]]'' revolves around one of Happosai's sins (insulting a witch by [[PantyThief stealing her undergartments]]) coming back to haunt all of the cast in the manifestation of a summoned spirit that is [[ImplacableMan implacable]] and, worse yet, [[AdaptiveAbility capable of adapting]] to all attacks [[ItOnlyWorksOnce that can injure it]]. By the time the Nerima Wrecking Crew finally figure out a way to kill it with magic in the final act, it is every bit as epic a battle to put it down as [[WhyWontYouDie you would expect it to be]].

SisterTrope to the TimeLimitBoss (when failing to defeat them in time is an instant game over), BossArenaUrgency (when the area the battle's taking place in is getting more dangerous) and MetalSlime (which costs the player a reward if it isn't defeated quickly instead). SubTrope to GatheringSteam. Contrast TurnsRed. Compare StalkedByTheBell and TimedMission, which share a similar relationship to this and Time Limit Boss. If you need to clear away your enemies' support to make things easier, you may need to ShootTheMedicFirst and / or ShootTheMageFirst. TheVirus (especially the zombieism variants, given that a lone zombie may not pose a great threat, but it will infect others if not re-killed) is often a meta example, as the longer it spreads the more victims fall to it (and the more of a threat it becomes).

* ''VideoGame/LethalCompany'': The Jester is a jack-in-the-box on legs that looks rather adorable while harmlessly following players around the facility it's in. After some time, it will stop and wind itself up to the tune of "Pop Goes The Weasel". Once it finishes, its true, [[SkullForAHead skeletal head]] pops out and it gives chase to players, [[OneHitKill instantly chomping and killing]] those it catches and moving to the next. It knows where each and every player is within the facility, while also [[GatheringSteam getting faster and faster]] the longer it stays in this mode, eventually catching up to players within seconds. The only way to stop it is to have every surviving player leave the facility, which resets it back to its initial state.

* ''Junkworld'' has enemies called Abominations, mutated stags with moderately high HP and low attack which will attempt to mutate further after losing half their health. If they don't die before they finish mutating, they turn into Abozombies, two-headed humanoid deer monstrosities that have ''far'' more health and attacking power.

** In a different sort of [[VillainProtagonist enemy]], the Bio-Weapon plague will get increasingly deadly no matter what you do, and quickly becomes so quick at killing it can't infect fast enough and burns itself out. The key is to keep [[WillfullyWeak developing supression genes that will keep the lethality down]] for some time at least, until you've managed to infect enough people. And, if you infect everyone, you can just bring back ''all'' the lethality back [[OneHitKill and then some]] by unlocking the Annihilation Gene, which can and will kill the world in two weeks if everyone's caught the disease.

* ''VideoGame/{{Xenogears}}'' has an enemy in the Shevat shafts called the Forbidden, a [[LizardFolk lizard man]] chained to a rock. They have 500 HP and cannot attack initially, but if a few turns pass, they break out of their chains as a 9000 HP monster and start attacking with a move that [[SituationalDamageAttack deals damage equal to their lost health]], which can kill party members quickly.

* ''VideoGame/{{Xenogears}}'' has an enemy in the Shevat shafts called the Forbidden, a [[LizardFolk lizard man]] chained to a rock. They have 500 HP and cannot attack initially, but if a few turns pass, they break out as a 9000 HP monster and start attacking with a move that [[SituationalDamageAttack deals damage equal to their lost health]], which can kill party members quickly.

** Some bosses apply debuff stacks. The most famous of this are the bosses from Aurum Vale, which require consuming respawning Marbol fruits during the fight to stay alive

* In the remake of ''VideoGame/ResidentEvilRemake'', dead zombies who are not [[RemovingTheHeadOrDestroyingTheBrain decapitated]] or [[KillItWithFire burned]] will later come back to life as deadly [[DemonicSpiders Crimson Heads]] when the player returns to the area after a certain amount of time or if certain {{Event Flag}}s are triggered (although, there's at least one corpse that the player can't do anything about, and a boss battle with the SuperPrototype crimson head that can't be avoided).

* In the remake of ''VideoGame/ResidentEvil'', dead zombies who are not [[RemovingTheHeadOrDestroyingTheBrain decapitated]] or [[KillItWithFire burned]] will later come back to life as deadly [[DemonicSpiders Crimson Heads]] when the player returns to the area after a certain amount of time or if certain {{Event Flag}}s are triggered (although, there's at least one corpse that the player can't do anything about, and a boss battle with the SuperPrototype crimson head that can't be avoided).