Story-Driven Invulnerability

You open the Locked Door, and find yourself staring at the level's boss face to face. However, instead of the battle immediately commencing, he taunts you, begins to run away, and exclaims that if you want to fight him, you'll have to catch him first. As you chase him throughout the subsequent Death Course, evading enemies and negotiating obstacles, you notice that the boss is in plain sight. You whip out your Weapon of Choice and unload on him, but he doesn't die. In fact, he appears to take no damage whatsoever. You find that it's not until you reach the Boss Room and the Boss Battle officially begins can you successfully deal damage.

What happened? The boss had been granted Story Driven Invulnerability, which occurs whenever a character is rendered invincible simply because the story decrees that they aren't supposed to be killed yet, even though they logically should be susceptible to damage.

This can occasionally be justified with the presence of bulletproof glass or something of that nature, or perhaps the target is only exposed for a time just a second under the time it takes you to fire off an attack. However, you'll find that much of the time no Hand Wave exists. Your attacks will hit but simply not register.

A subtrope of this is Gameplay Ally Immortality. See also Hopeless Boss Fight, where there's usually a reason or Hand Wave for their invincibility.

"Arkantos: You always seem to be hiding behind something when you face me, cyclops."
 * In Golden Eye 1997, in the Elaborate Underground Base level, the Big Bad is standing right in front of you at the level's start and promptly runs the heck away. If you use a cheat code to freeze him in his tracks, you can literally shoot him a hundred times in the face with the Golden Gun and he'll just keep standing there, flinching occasionally but never actually dying.
 * Averted in the final level. You are supposed to chase Alec around the level shooting him until he challenges you to a final shoot out, however if you blew him up it was possible to knock him off the stage, instantly killing him and triggering the end of the game.
 * Also averted in the Silo level. If you're quick enough to pop Ouroumov with the golden gun, it will kill him and leave his keycard and briefcase for you to take - neither of which has any in-game use.
 * The Grand Theft Auto games feature this constantly. You're often supposed to chase down somebody, but their cars will be completely impervious to your bullets. You can't kill them until you reach a cutscene and the story says its okay.
 * A specific example of this is the last "Revenge" mission of Grand Theft Auto IV: when chasing down on-foot, players can try firing a rocket launcher into his getaway boat before he gets into it. Instead of it exploding like all vehicles do under normal circumstances, it just triggers the in-game event of him getting in and speeding away.
 * San Andreas has the "OG Loc" mission, where you can shoot at Freddy while chasing him by motorcycle, but you can't actually kill him until after the chase.
 * Another example in Grand Theft Auto IV was when an enemy needed to be chased through a warehouse to to the rooftop where the player needs to shoot down the helicopter that comes to pick him up. At several points the enemy NPC got stuck on parts of the scenery long enough that several clips worth of ammunition could be emptied into him with no effect whatsoever.
 * Averted at one point in San Andreas, an assassination mission can be made significantly easier by shooting out the tires of the target's getaway car before the mission begins.
 * GTA IV is particularly egregious as there are more than a dozen missions where the target vehicle is invincible until it passes a certain point in the map, at which point it abruptly becomes vulnerable and you need to blast it to bits to finish the mission. The annoying thing is that the game never indicates (i.e. with text or a cutscene) when the vehicle has suddenly become vulnerable, leaving you to simply shoot at it intermittently during the chase until it actually starts taking damage.
 * At least with the games running on the GTA 3 engine some dedicated players have turned this into their advantage by figuring out methods to gain use of the bullet/flame/explosion/collision-proof cars. Some common aspects are that otherwise indestructible cars are still vulnerable to being run over by a tank, and pushing the charred wreck into a garage will restore it once the door closes. The garage will also unlock the doors of the car, and vehicles like these are usually locked to prevent player use.
 * GTA Vice City averts this in the final mission-.
 * In Condemned: Criminal Origins, the first half of the game is spent following a deranged killer through various rundown buildings and an abandoned subway station. You often get glimpses of him as you track him down, and there's at least two specific points in which you actually get a good look at him and have an opportunity to shoot at him. He is, of course, invincible.
 * The bullets don't go elsewhere for Half Life's G-Man. They bounce off him. Seriously.
 * Considering who he is, it isn't unreasonable to assume that he's actually immune to them.
 * Creepily enough, in the first game, bullets made the "metal richochet" noise when they hit him...
 * Famously averted in Metal Gear Solid 3. The fight with The End can be bypassed entirely if you manage to snipe him in a blink-and-you'll-miss-it segment long before you are intended to boss-fight him. He dies from one bullet (in the actual Boss Battle, he can take half a dozen to the head) and the zone where you'd usually fight him is filled with Ocelot soldiers, which, depending on the player, might make the fight even harder. Be aware, if you decide to try this, that The End's camo and gun become Lost Forever, since you never properly fight him.
 * Also, you can damage during the chase scene that precedes the boss fight, but the chase scene isn't long enough for you to take away more than 1/4 of its life.
 * However, if you kill Ocelot, you get a Nonstandard Game Over for causing a "temporal paradox".
 * Played straight, however, in Metal Gear Solid. Shortly before fighting REX, the player can look at through the scope of the PSG 1. Firing the rifle does nothing to stave off the "final" battle.
 * Also played straight in Metal Gear Solid 2 with Fortune and also.
 * FEAR does this with its dragon. Although it's usually justified by the presence of bullet proof glass or similar, the first time you meet him you can still shoot him and find that it does nothing.
 * The Elder Scrolls uses this trope in Oblivion and Skyrim. Many characters, that are important to a quest, cannot die. If their health reaches zero, they simply fall unconscious and stand up after a short while.
 * This can be hilariously abused by the inventive player, since if a "follower" will engage enemies that attack the player, a plot-relevant follower can be dragged through all the planes of Oblivion (we've nearly reached your farm, honest!) and be used to clear out entire areas on their own.
 * During the first quest (Unbound), your follower cannot die. This can be exploited to train your weapons skills right in the beginning of the game.
 * The system includes functionality for removing the invulnerability, but it is not always used, and some quest-important characters are important to background functionality or pragmatic design, meaning they never cease to be important to a quest even when the apparent quest has been completed.
 * Twenty Twenty Seven: Only Xander is invincible when you are in the same room as him. Other characters can be killed whenever, but they are usually in locations that prevent you from killing them.
 * Seen in the LOOTERS! chases in Beyond Good and Evil: The looters are invincible until you catch up with them at the end of the chase, where they die in one hit from the neutralizing cannon.
 * The The Incredible Hulk Ultimate Destruction does this with the Abomination near the end of the game. You chase and attack him, while the military attacks both of you, but the Abomination is completely invulnerable until you reach a certain destination where he will then turn to fight you and gain a health meter. After depleting the his health meter, the cycle repeats a few more times.
 * In Sonic & Knuckles, during the Cutscene in which Robotnik steals the Master Emerald, the player has full control of Sonic and can attack. Robotnik's craft even reacts to hits as if it was taking damage, and there's enough time to hit him eight times, but it cannot be destroyed--even though you'll encounter this particular craft again near the end of the game, as the last segment of the sometimes-final boss battle, at which point eight hits will destroy it.
 * Glitch exploitation eventually allowed an inquisitive player to put Robotnik's apparent invincibility to the test. The hovercraft boss model isn't actually invincible, but has its health set to 255. Hitting it 255 times via glitching caused the model to explode like a normal enemy. Of course, Robotnik still reappeared at the next cutscene point right-as-rain.
 * After beating Silver Sonic in Sonic 2, Robotnik will flee from his control room into the cockpit of the final boss. Despite being the fastest thing alive, you cannot catch up to him; he will magically speed up if you are too close, even if you spin dash at him. You'll probably see it a lot, too.
 * The first Sonic the Hedgehog on the Genesis\Mega Drive had you chase Robotnik up a Death Course with rising water (and the fireballs go through the lava!) It's hard to get hits on him, and he acts like he's getting hurt, but he just leaves after you finish the death course.
 * It's actually totally possible to 'defeat' Robotnik in the Labyrinth Zone -- if you can dodge every trap, aim your rebound from hitting him for minimal fallback, and successfully hit him eight times, all of which is insanely difficult, Robotnik's Eggmobile will begin to explode just as it does in every other boss fight. He will still, however, climb to the top of the shaft and run away. While exploding.
 * Similarly, you can destroy Robotnik's escape pod after the Final Boss battle, although it doesn't affect the ending.
 * In Halo 2, each time you damage the Heretic Leader, he retreats into the ventilation ducts to give a certain dialogue to the Arbiter, and during this time he is invincible. Most noticeable during the glitch where he gets stuck under the balcony, where after a minute, he turns into one of the holodrone spheres himself. Needless to say, he is also invincible if you try to shoot him while he's running to the shielded room.
 * It is possible to kill him in one round with the plasma sword if you're fast enough before his scripted invincibility takes effect.
 * There's a glitch where you can "kill" him on The Arbiter, however, it will cause you to be stuck in an Unwinnable situation, requiring you to restart the level.
 * Call of Duty 4, the final mission. You're given an RPG and told to fire on a Ultranationalist helicopter, but it has story-driven invincibility, since it's scripted to wipe out your squad at the end of the level, and is only destroyed by the Russian Loyalists when they arrive(too late for most of you). Interestingly, if you do manage to get a hit in with the RPG (which is the equivalent of hitting a needle in a haystack) while you're in the car, the game activates an alternate (and supposedly glitched) ending where an unnamed squad member comes out of the side of the screen, beats Zakhaev and his guards without them reacting in any way and stands around as the rest of the ending plays out in the same fashion.
 * It's the same with the Big Bad in the flashback mission. Even if you get a perfect headshot with the sniper rifle, the bullet will veer off and hit him in the arm.
 * In Soldier of Fortune II, in Vergara's Mansion, Sanchez is invincible until the end of the mission, and even then he can only be killed by blowing up the fusebox with a grenade, electrocuting him.
 * Bio Shock fits this trope to a T, when you're chasing at the start of the penultimate level. If you're quick, you can shoot him several times - but he has no life bar.
 * While MiG 1.44 can be "shot down" in the penultimate mission "Aces" of Ace Combat 5 The Unsung War in the sense that the player will receive credit for the "kill," he doesn't actually go down, as he has to tail and attack your flight throughout the climactic tunnel chase. (Since this is from behind, he's unattackable and can only be fought before destroying of the enemy ground targets and triggering the tunnel opening.)
 * In Ace Combat 04 Shattered Skies, the Yellow Squadron are invincible until the Stonehenge mission.
 * If you hit them in various missions (like the titular mission 8, Shattered Skies), they will comment, asking "who was it that shot me?" They only exit the battle, but you can't ever shoot them down until the mission at Stonehenge.
 * In Ace Combat Joint Assault  have the same deal; you won't actually kill any of them until the final mission.
 * From Wing Commander II onwards, instead of dying, as in the first game and its addons, your wingmen can always eject... unless the plot requires that they die.
 * You cannot kill Stephen Tyler in Revolution X. Aim right at him and fire those CD's to your heart's content, and he just ducks and looks stupid.
 * In Diablo II, when you go to defeat Baal, he just sits there and summons a few rounds of minions at you, while being completely invincible until the "real" battle with him begins in the next room.
 * Similarly, in the first Diablo, when you finally meet the Archbishop, he stands there and speechifies at you for a good while. Neither side can attack while he's talking, but you can run out of the room, which is recommended as he's accompanied by a number of minions and it's easier to kill him if you've lured them out piecemeal first.
 * In Medal of Honor: Frontline, Sturmgeist is invincible until the final level. In the Golden Lion level from the same game, a Panzerschreck soldier is scripted to kill your truck driver near the end of the level. He's within sniping range, but shots on him won't register before he fires.
 * At the very end of the 2009 Wolfenstein, after killing the final boss, you're teleported into a collapsing corridor where you have a clear shot at the Nazi Commander Big Bad as he flees away from you towards the exit. You can actually pump several bullets into his back if you're quick enough, but he'll just keep running and quickly escapes.
 * Quite a few bosses in World of Warcraft have this, the most notable being the Lich King. There are about a dozen quests and an event in a raid dungeon where he appears to talk with his minions or other things, but he can't even be attacked.
 * Several bosses in Ulduar and the Argent Coliseum can't be actually be killed, because they are actually good guys, either under mind control or simply testing your skills.
 * The Lich King also makes an appearance in the Halls of Reflection dungeon, where he can be attacked and dealt damage but not killed. In this case, Story Driven Invulnerability only applies to his last hit point.
 * In the first Spider Man game for the Playstation 1, Venom pulls this on Spider-Man, sneaking up behind the hero and leading him into a chase level. During this level, you have to move insanely fast to keep up with Venom, and it is very hard, for even though there is nothing that tries to kill you in the level, you lose if you fall too far behind. However, you can memorize or predict Venom's path beforehand (if you're crazy enough) and land right next to him on a few occasions, which case if you try to punch him or whatever, you have no effect on him.
 * Used in Assassin's Creed II. In a few of the secret tombs, you have to chase a lone guard through the tunnels, dodging traps and finding alternate routes throughout the environment as he desperately tries to evade you. The game disables your projectile weapons in these sections, and even if you get close enough to use your hidden blade the prompt to use it doesn't show up.
 * One of the assassination targets is a bodyguard who, before he is to be killed in the story, can be in a position to attack Ezio. He is completely unkillable (which sort of makes sense, given the framing device). He can, however, be knocked into water with some effort (which effectively eliminates him, though doesn't kill him plotwise).
 * In Syphon Filter, for no apparent reason (no full body armor here), Rhoemer is immune to bullets, even headshots and explosions, and can only be killed with gas grenades. Perhaps this is to prevent you from killing him too soon.
 * Similarly, with the fully-armored Anton Girdeux, the back of his head is unarmored, but you can't hit him there either. That would be too easy.
 * Variation of this in Time Crisis 4 when you're facing Jack Mathers (the second boss). At the start of each life bar, he'll mix it up with William Rush, during which he doesn't attack you at all. It's actually possible (and in fact pretty easy) to do the equivalent of a whole life bar's worth of damage in this time. However, you can only take off the green portion of the bar, about two thirds. The remainder doesn't turn green until he starts attacking you. Obviously this was done so all the action and dialogue between Mathers and Rush would be completed (and so there'd actually be some challenge to this battle, of course). This is true of the other bosses, but Mathers is the most blatant example. This also happened in Crisis Zone, and previous Time Crisis games, but that was just so the bosses would live long enough to use all their attacks.
 * In Kingdom O'Magic several characters are invulnerable, and not all are important - there are plenty of bit characters with minimal dialogue who are unbeatable. Specifically, all the elves are invulnerable, but none of the ringwraiths. Seeing as they'll actually fight each other if they wander into each other when you're on screen, you can actually eliminate almost all the wraiths simply by having elves whittle down their hitpoints.
 * Batlin in Ultima VII: The Black Gate is invulnerable since he's a badly concealed Dragon to the Big Bad, and they presumably wanted to avoid the option to end the game half an hour in. Lord British is of course always invulnerable to everything except certain glitches and loopholes.
 * In the 1998 FPS Sin, the main antagonist of the first three levels, a thug named Mancini, is being pursued by player character John Blade through a bank, a construction site, a series of city blocks and finally a subway. At several points during this chase, he is seen quickly before running away (usually with a hostage in tow), but if you're quick enough, you can snipe or shoot him, which won't cause any damage whatsoever. Most notably, the first encounter with the mutated Mancini has a period of several seconds where he pauses before jumping back into the ceiling, allowing you to run up and blast him in the face at point-blank range with a machine gun (to no effect).
 * In the second-last level, Elexis Sinclaire lures you into a trap when you attempt to walk into a room filled on two sides with bulletproof glass and a single entrance - it's possible to try a bank shot into the room just before you hit the trigger that drops the floor out from under you, but the entrance has an invisible wall.
 * The Big Bad of Age of Mythology always seems to be just out of reach when seen, always appearing on top of cliffs, on the other side of jail doors, across deep chasms, etc, etc. This is even lampshaded. However, if you do manage to attack him, somehow, you'll notice something. His special ability in his bio only says 'regenerates'. And he does. To the point where it takes an entire army to bring him down.


 * In one of the stages in Sengoku Basara 3 you must race Masamune Date on horseback. While it is possible to do massive damage to him with some tricks, you can only reduce his hit points to one, but you can't kill him. You can however kill his second-in-command Kojuro as you two race towards Masamune's position.
 * All bosses have an introduction cutscene before fighting them, which triggers when you move close enough. Prior to the cutscene, if you have ranged attacks, you can fire them until the end of time, the boss will stand here and wait when you come closer.
 * In Deus Ex Human Revolution, when you meet Taggart at the convention centre, no matter how much you may want to kill him, he can't die, even if you unload a full heavy rifle clip into him. He later loses this in, when you can kill him if you want.
 * In the Atari Star Wars arcade game, Darth Vader's fighter is indestructible, though it can be shot for points.
 * In Mass Effect 3, Dr. Eva during the Priority: Mars mission. At the end of the mission while you chase after her you can shoot at her but never inflict enough damage to kill her before she gets too far ahead and you lose. One cutscene later you get to "kill" her in slow-mo.
 * In Mega Man 2, you have to run away from the Mecha-Dragon for a short period before you can fight him. The game even broadcasts this point by having his life bar only appear after the chase.