A trope often seen in Video Games, these doors, treasure chests, barriers, and all sorts of locks won't open until someone kills the enemies surrounding them, as though the seal's integrity were somehow linked to the enemies' lives.
Usually the character has to kill every single enemy in the room/level in order to defuse the lock, but sometimes it might require just a percentage of them, or the elimination of a specific type of enemy like an Elite Mook of some sort.
Teleporting Keycard Squads have a tendency to invoke it when they appear, in order to force the player to fight them. Also quite common in Boss Battles, as way to prevent the players from escaping or "unfairly" exploiting the environment to their advantage. Beat 'em Up games often raise Invisible Walls that can only be bypassed this way. May induce Fake Longevity if abused or poorly implemented, as in games that hide enemies to force the player to backtrack.
This is sometimes justified: enemies might harass you when you attempt to open the lock; they might be a Strength Equals Worthiness test, so if you're strong enough to beat them, you're worthy to proceed; they might have keys you need to open the lock; or they might be actively maintaining the lock and defeating them disables it.
Compare and contrast the Gate Guardian, an enemy who personally prevents you from progressing, although these tropes can overlap.
Unrelated to Beef Gate, where the only thing stopping you from proceeding is the threat of imminent death on the other side. Compare and contrast No Ontological Inertia and Load-Bearing Boss, where defeating the enemy brings down much more than just a lock.
- Castlevania: Curse of Darkness has a few doors that will only open if you've defeated all enemies in the room. Unfortunately, one of these is in a room where the only enemies are Blood Skeletons which resurrect a few seconds after being defeated. How do you defeat them? Bring one of your Innocent Devils who has the ability to permanently kill Blood Skeletons. For your trouble, you get an item that increases your Max HP.
- In Chantelise, barriers prevent you from moving onto the next level unless you have cleared it at least once.
- Most of the games in The Legend of Zelda saga make use of this trope. Usually, the locks activate after you find an important treasure, or just before you get said treasure. The Legend of Zelda: Breath of the Wild has a variant with certain monster camps which contain a treasure chest that can only be opened when all of the monsters have been defeated.
- The Metroid series uses these a lot, usually in the multiple pirate bases you'll have to raid.
- In Owlboy, wiping out all the enemies in some particular areas will make a treasure box appear.
- Star Fox Adventures has its own share of Life Force Doors. They look like red vortexes with a skull in the middle and little "spirits" orbiting around it. That last detail actually has a purpose, as the number of "spirits" indicates how many enemies you need to kill to open it.
- Red doors in Ittle Dew must be opened by killing enemies, unlike green doors which use puzzles.
- Luigi's Mansion:
- Nearly every first-visited room in the first game requires Luigi to suck up all the ghosts in it (not counting hidden Boos) in order to get rid of the supernatural vine barrier thing that protects every door.
- In Luigi's Mansion: Dark Moon, there's a moment during the third mission of the fourth area (Secret Mine) when three powered-up ghosts seal the entrance to a cableway car with magical energy chains. These chains are linked to the life force of the ghosts, so Luigi has to hunt them down as he revisits previous rooms.
- Luigi's Mansion 3 does this rarely, preferring instead to employ scripted ambushes where Luigi has to capture all ghosts in order to dispel the life-force barriers that prevent him from leaving the current room.
- Diablo III: Several random events involve "cursed chests", which glow with a red light and trigger an attack of enemies when you click on them, who must be defeated to open the chest.
- Fortune Summoners: When passing through a level the first time, the way out cannot be used if monsters are near you.
- Black★Rock Shooter uses two flavors of this trope, with varying requirements:
- Parts of the stages will sometimes be blocked by a red sigil named Territory Seal, requiring you to defeat the armaments with a red kill mark before proceeding.
- There are also Territory Box barricades that require you to destroy every armament in the area.
- SoulBlazer has this as a core gameplay element. Stepping on a Mook Maker after killing all of its monsters will usually clear away some nearby obstacle or release some sort of NPC.
- In Project Altered Beast, some parts of the levels are locked unless you beat the specific enemies called aptly "Gate Keepers". They're just variants of the common mooks, but with a Battle Aura and more resilience; they also don't respawn unlike regular mooks.
- Fire Emblem Warriors: You'll occasionally come across large gates that are closed and prevent you from going through. To open them, you need to find and kill a specific Captain, usually a Gatekeeper. Barring those, Fort Captains will do.
- In the Paper Mario games: The Thousand Year Door and Super Paper Mario have the "Pit of 100 Trials", where Mario and his companions face off 100 rooms with enemies (either in an RPG turn-based battle of the former or a Platform Game kill enemy battle for the latter). In TTYD, you must beat all the enemies to make a pipe to the next lower level appear. In Super, you just have to find and kill the mook that's carrying the key that unlocks the door to the next room.
- Science Girls!: The starting area is the 5th floor of the school, and lower floors are unavailable until all the 5th floor rooms are explored, meaning, all the enemies inside them have been killed.
- In the Doom games:
- The only way to reach the end of the Phobos Anomaly in Doom is to kill the two Barons of Hell that serve as the bosses of the level. Doing this will open the way to the outside where the exit is.
- Doom II's level "Dead Simple" starts the player inside a cloister with four mancubi, each one on a raised platform. Once all four mancubi fall, the outer walls lower to reveal a fleet of arachnotrons in the outer perimeter. Every spider must also be killed in order to make the platform that leads to the exit rise.
- DOOM (2016) has a lot of areas under lockdown due to the demonic presence, and that need to be cleared of demons in order to advance.
- Whenever a battle starts in the God of War games, every possible escape route is covered with a wall of flames. The flames vanish after all enemies are slain.
- Doors in the Devil May Cry series sometimes become locked with magical barriers, requiring you to kill all the demons in the room before proceeding.
- Bayonetta and Bayonetta 2 both use orange-colored barriers that obstruct the progress whenever the eponymous protagonist is ambushed by a group of angels or demons. Interestingly, when all enemies are dispatched, an animation displays Bayonetta breaking the barriers with a blown kiss.
- EverQuest had a variation on this. The insanely powerful but mostly insane prismatic dragon known as Kerafyrm was put to sleep by Veeshan, the God of Dragons for his crimes against dragonkind. The catch was that four dragons had to spend the rest of eternity as warders to ensure that the spell keeping him asleep was never broken. Players had to kill all four warders in order to wake him up... but the first few guilds in the game to do so quickly found out that waking him up was a bad thing. Kerafyrm would rampage out of the tomb, go over to the city of Skyshrine and go on a rampage there, and then go on a rampage in the Temple of Veeshan before finally leaving for good. This happened once and ONLY once per server. The Warders, who contained exceptionally powerful loot, were dead for good.
- Justified in EVE Online as enemy ships carrying jammers for the acceleration gates which separate mission pockets. Kill the enemy ships and the jamming stops so you can proceed.
- Elsword: This is pretty much inherent in the game system: You can't get to the next area in any dungeon unless you killed all the mobs in the current area first.
- In World of Warcraft, The Burning Legion is very fond of soul-powered portals. To use them, you either need to kill something with a powerful enough soul (multiple not quite as powerful souls work too) in the vicinity of the portal, or bring souls with you for it to burn through. Most player characters and friendly NPCs opt to Pay Evil unto Evil and kill demons in the portal's presence, subjecting the demons to a very well deserved case of Hoist by Their Own Petard.
- All boss segments of Final Fantasy XIV seal off the back exit until the boss is beaten, and the front entrance shortly after the boss is aggro'ed, the latter so people can't circumvent the Weakness penalty upon being Raised/Resurrected, or the need to be raised altogether, by respawning and running back down the dungeon hallway into the fight. There are also frequently spots along the hallways that block progress until some nearby mob/s is/are killed. This is usually a blatant device to prevent players from pulling all the tedious trash mobs between bosses at once and Ao Eing them to death, getting the tedious hallway cleared in a timely fashion.
- Realm of the Mad God:
- The portal leading to Esben's Inner Sanctum is only opened when all Big Yetis and Snow Bat Mamas in the Ice Cave have been killed.
- The wall separating the rooms of the Marble Defender and the Marble Colossus will vanish only when the Marble Defender is killed.
- Killing the Agonized Titan opens the portal to the Cultist Hideout where Malus, his colleagues and their followers hide.
- Several enemies Item Drop Mechanics have them drop portals to restricted areas when killed: the Stone Guardians drop the portal to Oryx's chamber, while Janus the Doorwarden drops the portal to Oryx's court.
- Janus himself resides in a locked room that only opens when all the Living Statues in the Castle are destroyed.
- In Rayman Origins in order to rescue the Electoons, you need to dissipate bubbles of dark energy surrounding them by killing the enemies connected to it, (as it seems their life-force is the thing powering the barrier via streams of darkness) before smashing their steel cages to bits.
- In Sonic Rush, some acts will trap the player in a certain area where several enemies appear. The player must then defeat all enemies to escape and continue through the level, with a counter showing how many of them are left.
- Spyro the Dragon:
- In the second and third Spyro the Dragon games, on each level you need to defeat a certain number of enemies before special pedestals with powerups become active.
- The Legend of Spyro reboot of the series does this a lot, often with an Elite Mook summoning an Elemental Barrier in order to make a sort of cage match where you have to beat every enemy to proceed.
- A few instances in the Super Mario Galaxy games require Mario to beat all Mooks nearby in order to make a warp pipe or launch star appear. In the second game, this is the driving concept of Battle Belt Galaxy.
- Donkey Kong 64. Sometimes you have to beat every enemy inside a certain room in order to have golden bananas, switches or bonus barrels show up. A few times, doors are unlocked as well.
- Conker's Bad Fur Day has two examples: A wooden door in the Windy area that opens when the eponymous character kills the big beetles guarding the access to the Poo area (though the door leads to the Barn Boys chapter instead, the Poo zone is open otherwise); the other is a door in the War chapter that opens when a large group of Tediz is dispatched with a gun turret.
- Treasure Hunter Man 2: The room in the cave at the far bottom right of the "Windmill at the End" has a door at its top that needs the death of all the monsters inside to unlock it.
- Hyper Princess Pitch: Your goal is to Shoot Everything That Moves in Mecha Santa's factory, one room at a time. The doors to other rooms only open after all the enemies in a room are destroyed.
- Kirby Star Allies: Some levels have chokepoints in the form of a Multi-Mook Melee, with respawning mooks and sometimes minibosses, which Kirby and co. have to defeat before they can progress.
- Dawn of War 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.
- Dungeon Keeper 2: The final level's Portal Door out of the underworld can only be opened by collecting Portal Gem Mineral MacGuffins from throughout the game and then destroying the two Stone Knight Gate Guardians that bar passage by the forces of Evil. They're Nigh-Invulnerable, but by that point, you have enough villain cred to summon a Horned Reaper that pounds them to dust in a Cutscene.
- The Binding of Isaac makes ubiquitous use of it, as every room containing enemies will automatically shut itself down until you kill them all. 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... Just like every single door in the game's Brutal Bonus Level.
- A staple in the Mass Effect series, where you usually required to clear out each room before you are allowed to proceed.
- In Fable I:
- The Hook Coast connection in the Cullis Gate Portal Network is a Broken Bridge that requires the Hero to destroy a wave of undead near the Darkwood's Ancient Cullis Gate, reactivating the Gate with their Life Energy.
- One of the Demon Doors believes that Strength Equals Worthiness and only opens for a Hero who can defeat all the waves of progressively stronger Hobbes that it summons.
- At the beginning of the "White Balverine" quest, Knothole Glade is locked down and won't open its gates until the Hero defeats the waves of Balverines in the forest outside. Justified since the gates are there for that specific purpose.
- Near the end of the main quest in The Elder Scrolls III: Morrowind's Tribunal expansion, you'll need to defeat the "Imperfect", a humongous Fabricant who guards the final room in the Clockwork City. You won't be able to open the door to the final room until the Imperfect has been slain. Notably, this trope is often averted elsewhere in the game, as it is perfectly reasonable to sneak past enemies and pick locked doors. (The game has very few Plot Locks.)
- Vampire: The Masquerade Bloodlines: When the Mandarin kidnaps the fledgling vampire Player Character to test how Our Vampires Are Different, one hapless Mook is Trapped in Containment with the vampire and a wholly ineffective crucifix. Unfortunately for the Mook, killing him is the only way to open the chamber door and advance the quest.
- During Slime Rain, killing 150 slimes summons King Slime. If you've done it once before, only 75 are needed.
- During the Lunar Events, in order to damage a Celestial Tower, one must first kill 100 enemies (150 in Expert Mode) from within its section, which removes the shield that protects the Tower and makes it vulnerable to attacks.
- Bangai-O Spirits use special blocks that have an arrow icon pointing at a specific direction of the level. These blocks will only break when all enemies and targets located within the range and width of that direction are eliminated. For example, a block whose arrow points to the left will be protected by the life force of the enemies located at the left, upper left and upper down areas of the level. A block whose arrow points to the bottom right will break when the player destroys the enemies found at the bottom, right and bottom-right areas. This can be used cleverly in custom levels to make some ingenious mazes.
- Rock Solid Arcade's Web Games Robokill and Robokill 2. When you enter a new room there are no exits. You must kill every opponent in the room before the exit(s) will open.
Non-Video Game Examples:
- In Mighty Morphin' Power Rangers: The Movie, the rangers encounter a large stone door that blocks them from reaching the "great power" stashed in the monolith on the planet Phaedon. On the door are four life-sized carvings of warriors that come to life to fight the rangers. It's only after the stone warriors have been dissolved, disintegrated, or crushed in combat that the door finally opens.