History Main / KillEnemiesToOpen

* ''VideoGame/DawnOfWar II: Retribution'': When trapped on Typhon in the Deranged Chaos Champion's arena, the barriers around the arena will only fall once you kill the Champion, and he only emerges after you kill a sufficient number of orks, chaos forces and tyranids that continuously pour into the arena.
* ''VideoGame/DungeonKeeper 2'': The final level's PortalDoor out of [[BeneathTheEarth the underworld]] can only be opened by collecting Portal Gem {{Mineral MacGuffin}}s from throughout the game and then destroying the two Stone Knight {{Gate Guardian}}s that bar passage by the forces of Evil. They're [[NighInvulnerability Nigh-Invulnerable]], but by that point, you have enough villain cred to {{summon|ingRitual}} a Horned Reaper that [[spoiler:pounds them to dust in a {{Cutscene}}]].

* Taking its cue from the dungeons in ''Franchise/TheLegendOfZelda'', entering any room containing enemies in ''VideoGame/TheBindingOfIsaac'' results in every door locking (including the one you came in through) until you kill them all. Challenge rooms, which are initially empty, have the doors seal if you accept the challenge and spawn the enemies in. However, the game also features a twist to it, as it's possible to force your way out of a room containing enemies by blasting the door with a bomb. (Either yours or fired by an enemy). Of course, this tactic must be used sparingly because bombs are a precious commodity most of time, and doing so doesn't take care of the enemies inside the room, so if you walk back into it, you'll either have to deal with the enemies, or use another bomb to escape once again. Also, this tactic doesn't work in boss' (nor mini-boss') battles, because their doors are blast-proof... [[spoiler:Just like every single door in the game's BrutalBonusLevel.]]

* ''VideoGame/StarFox'':

** The second of the InterchangeableAntiMatterKeys in Squid Baron's location, requires Shantae to defeat all the enemies in the previous room from the key's chest's room to unlock the doorway she came from when she was going to get the key.

* ''VideoGame/ShantaeAndTheSevenSirens'': Dungeons have rooms that lock on entry and unlock on defeat of all enemies, before important items like InterchangeableAntiMatterKeys.

* In ''[[VideoGame/AlteredBeast Project Altered Beast]]'', some parts of the levels are locked unless you beat the specific enemies called aptly "[[GateGuardian Gate Keepers]]". They're just variants of the common mooks, but with a BattleAura and more resilience; they also don't respawn unlike regular mooks.

* ''VideoGame/{{ULTRAKILL}}'' zig-zags this trope constantly, with some encounters completely abiding by this rule, and other encounters allowing the player to completely ignore every enemy and still proceed. Some do both, by locking the main doors but offering side passages out. And others still pull some ''evil'' tricks using the Idols (which turn an enemy into an InvincibleBoogeyman until destroyed) by locking them away behind barriers that will hold until you kill everything ''else''.