Lord British Postulate

""If it exists as a living creature in an MMORPG, someone, somewhere, will try to kill it.""

- Mike Schramm, WoW Insider

In short, if you as a game designer want an invulnerable NPC, make sure that it actually is.

The Lord British Postulate was coined in this WoW Insider post, and is the cornerstone of the creativity and ingenuity of the more cunning player. In short, if a NPC cannot be killed through normal means, then there must be some abnormal way to do the job. Quite often, if a character's weapons fail to do the duty, then the task falls upon other NPCs, world objects, or the environment itself to assassinate the relevant target, with some prodding from the player characters. The Lord British Postulate is not restricted to MMORPGs, but can be applied elsewhere: CRPGs, FPSes, even Tabletop RPGs.

That said, the Lord British Postulate has less grounding in reality than one would assume. A great deal of NPCs are free to walk around unmolested, safe in their invulnerability. However, the more important the NPC is, the more likely it will be the target of a creative assassination attempt. A king is a bigger target than the common baker, and much more satisfying to dispatch.

This trope can be an applied form of Loophole Abuse with how you go about killing Lord British Postulate.

Genre Savvy developers will actually code in what happens if you do manage to defeat them.

Contrast with Invulnerable Civilians. A Hopeless Boss Fight or Invincible Minor Minion is seen as a challenge to these people. This has nothing to do with the other ship from Gradius.

Fighting Games

 * In Soul Calibur III, the subboss Ceres is supposed to be unbeatable (you are told to endure the battle until time runs out without getting killed) but it is possible to beat Ceres if you attack very quickly and break his guard. Probably because the game designers didn't intend you to beat him, nothing special happens after you do.
 * Fighters Destiny and its sequel have a minigame where the objective is to stay in the ring as long as possible against a seemingly invincible bull. In reality, the bull can fall off the stage, though if this happens the round ends as if you did.

First Person Shooters

 * In Golden Eye 1997, a glitch involving using two controllers at once allows the player to fire on characters during cutscenes from the camera's perspective, instantly killing any that are hit. This includes Baron Samedi during his The End - or Is It?? moment. This has no gameplay impact whatsoever, though.
 * The Jedi Heroes in the first Star Wars Battlefront game were invulnerable to normal weapons; they would deflect blasters and simply get knocked down by splash damage. It is possible to kill them by using grenades or heavy weapons to knock them into environmental hazards: off the edge of Cloud City, into the Sarlacc pit, or into the Carbonite Freezing chamber. It is also possible to kill them by landing aircraft on them or ramming them them with a speeder bike.
 * An even easier method is to get them between a few turrets firing at the right rate. The flinch effect will keep them immobilized long enough for you to take them out. Sadly, they'd just respawn like Agents in The Matrix.
 * You could (if I recall correctly) also do this by using a vehicle to push said Jedi off the playable area; though this will kill you eventually, it'll also kill the Jedi, which will (for whatever reason) not damage your vehicle whatsoever. This works great with the Galactic Republic's tank.
 * Deus Ex has plenty of invincible NPCs, but many can be killed due to a collision bug. Get one to stand on the edge of a piece of furniture, then push the furniture against a wall; they will pass partially through the wall, and then die instantly as they game seems to think they've been crushed.
 * Prior to being patched out, it was possible to kill Eli Vance in Half Life 2. The player's attacks don't hurt him at all... but if you grabbed a sentry gun from earlier in the level, carried it all the way to Eli, and set it down facing him, it would quickly blow him away.
 * Another fun thing to do? Start a new game, get God mode going, Get the HEV suit THEN use Impulse 101 running. Get ammo and the crossbow, and follow the steps up to the teleport cutscene. As you are transporting from place to place, you can headshot Breen either place; when he first sees you and you fade out, or when he rounds his desk.
 * The physics engine can be exploited to kill certain otherwise-invulnerable NPCs using the Gravity Gun and nearby physics objects, and done at the proper times, you can avoid triggering a Nonstandard Game Over where you would otherwise receive one. Observe.

MMORPGs

 * Lord British, of course, from the Ultima series, who just happens to be one of Richard Garriott's two in-game Author Avatars. The postulate itself stems from a time during the Ultima Online beta test where, following a crash, Lord British forgot to set his invulnerability flag when he signed back on, and a player killed him with a hastily-stolen firefield spell on the spur of the moment during a public gathering.
 * A special pair of leggings were introduced to "commemorate" the event.
 * There was an event during the early weeks of Tabula Rasa that was about killing General British. Well, clones of him, actually, there were dozens of them.
 * Most NPCs in World of Warcraft are actually killable to players of the opposing faction, including racial leaders such as Thrall, Jaina Proudmoore, and the like. However, most NPCs in the neutral city of Shattrath should be invulnerable, as combat from players is forbidden there... unless, of course, one pulls an enemy from outside of the city into it and lets them run loose on the population. The main NPC of the city, a massive naaru named A'dal, was killed in this way several times until it was buffed to nigh-unkillable levels. It seems that the original A'dal had very few HP.
 * It's still possible to kill A'dal with a quest mob that becomes immune to everything at 50% health (you need a quest item to kill him). It just takes a very very very long time. In theory, it would also be possible to kite said mob to A'dal, then kite him away, effectively kiting A'dal itself (and every guard in the city). There is a rumor of this being done, but there are no videos to back it up.
 * The pre-launch event of the second expansion involved an infection that would turn player characters into zombies that were hostile towards everything but each other. You can use this opportunity to kill NPCs that were otherwise unattackable to both factions.
 * In the third expansion, one guild managed to kill Tirion Fordring by luring a mini-boss from earlier in the dungeon to him.
 * Invoked with the Whale Shark. An immense boss mob with no loot of any kind and the ability to literally one-shot anybody that attacks it, Blizzard had to add an achievement for killing it because so many people wanted to.
 * Some players expand this to include other players when not in PvP situations that allow deaths. Duels end with the other player having one hitpoint, but using knockbacks or mind control during the duel it is possible to kill via fall damage.
 * Perhaps the worst incident of this behavior was the Corrupted Blood Plague. Players discovered they could bring a highly-contagious disease to their home cities, where it would promptly spread and kill characters who were ordinarily protected from other players.
 * Early in the Mists of Pandaria beta there was a bugged version of Chi Wave. The spell is supposed to bounce between PCs and NPCs healing if friendly, damaging if an enemy. Earlier versions bugged so it would damage all NPCs.
 * In Guild Wars, a well-placed herd of Necromancer minions can sometimes kill exactly the wrong person during a mission cutscene.
 * The Eye of the North expansion is far more explicit with this. If an allied NPC is killed, it will either return hale and hearty on the next dungeon level or, more commonly, wait until its aggro circle is clear before standing back up, dusting itself off, and running back to your location. Quite a few NPCs will rubberband back up to about 30% if their health drops below this threshold, even if the damage they receive puts them deep into negative health. Of course, it was possible for decorative player minipets and certain resurrection NPCs to be accidentally killed by rolling ice boulders when they shouldn't, but this was quickly patched.
 * One month it was discovered that a specific buff could be used to spawn minions in some outposts by gaming to system slightly. As players do not have access to skills in outposts, the minions would quickly kill them, and their corpses would spawn more minions.
 * Kerafyrm the Sleeper, the Sealed Evil in a Can from the "end" of the original EverQuest. He was supposed to be unkillable, but on one server he was eventually taken down by a group of over 200 allied players in a battle that lasted three hours.
 * Also a particularly lasting example of Lost Forever—Kerafyrm could only be awakened once per entire Server, meaning a failed attempt prevented all others on the server from ever being able to do the event.
 * The issue here is that Kerafyrm was specifically designed to appear to be killable, so people would trip the sad story event caused by the failure. People were supposed to think they could win, and be on the end of a giant Player Punch when they inevitably lose. They couldn't make him actually unkillable, because once the first group to wake him found out, no one else would do it, because there is no benefit from trying and failing.
 * And while we're on the subject, Verant had to make characters used in GM events untargetable specifically because of this problem.
 * Yohoho! Puzzle Pirates has El Pollo Diablo, the black ship that appears if players attack ships weaker than themselves too often. It can't be shot, and it's crewed by (noq) 150 skeletons, but it has been defeated multiple times, each matched by a severe upgrade by the developers...
 * ... Except the one time they accidentally botched the ship to be crewed by just 8 skeletons.
 * Further, the hardest defeat so far, 100 skeletons versus a full Grand Frigate of top players, had one of the Game Masters fighting on the Black Ship, for full Lord British Postulate goodness, no less!
 * They are mostly beaten through boarding and stalling.
 * In the MMORPG RuneScape, one update brought a seemingly invincible enemy called the Vyrewatch. They've got a combat level, so they must be killable somehow, right? Someone went to the trouble of getting one to attack him while a group of friends dropped him rings of recoil and massive amounts of food. Eventually, the Vyrewatch died, with no death animation and no drops, proving that they really were intended to be invincible.
 * They're now killable if you use a weapon you get from the Legacy of Seergaze Quest.
 * And likewise, Runescape used to(?) have random events that would punish you if you were botting or doing nothing but practicing a gathering profession for hours-on-end. River trolls would attack fishers, wood spirits would attack woodcutters, and golems would attack miners. They were intended to be invincible to kill the player and force them to drop all their items (thus punishing botters) but people would actually turn around and kill their attacker, which would often drop something (But nothing really good, mostly bones or something like a fishing net that you likely already have or don't need)
 * Final Fantasy XI has the ostensibly killable Absolute Virtue, which does in fact have death animations, text, and very valuable (and exclusive) drops... but every time it's been killed so far, Square Enix respond with something along the lines of "No, that's not how you kill it" and patch it. Sometimes they ban the players who killed it, too.
 * Also notable is the actually newsworthy superboss Pandemonium Warden. When it was first patched into the game, it was deemed truly unkillable, and one linkshell group spent 18 consecutive hours in a single fight against it and could not continue. Since then SE patched it to make it actually very possible to kill, but it is still comparable to Absolute Virtue in difficulty.
 * City of Heroes had the Hamidon, a giant blob monster, which was similarly very difficult to kill. For the first year or so, players kept coming up with strategies only to have the Devs change the rules. Eventually the players found an "acceptable" strategy and raiding began in earnest.
 * CoH also had Riechsman, who was supposed to be completely invincible... however, when he first came out, he was still susceptible to Sleep abilities, which, while not killing him, completely mitigated him. Also, later on in the same set of missions, you get the means to defeat him... which you can keep, then do the story over again, and use the same weapons to defeat him when you're supposed to be helpless against him!
 * The Rikti Invasion events in City of Heroes featured dropships, which the dev team made virtually unkillable, with oodles of hit points, powerful attacks, and a tendency to simply fly away and escape before anybody can kill it, and which give no rewards for defeat, specifically because they were not intended to be defeated. When the Issue that introduced the Invasion events was in beta, a group of players took this as a challenge, banded together, and killed nine of them. The devs then made them even tougher, but still not unkillable.
 * In Champions Online, Justiciar in Canada is positioned dangerously close to a pair of explosive barrels which respawn. So long as no one's Nemesis minions show up to draw him into combat (and thus full heal him when he returns to his default position), a persistent player can kill him with the explosive damage from the barrels.
 * Another instance of this were statues in one of the endgame lairs. These statues were immune to all damage types, and shot lasers out of their eyes when approached, which the player had to use a mirror to reflect back at the statue to destroy it to progress through the lair. However, characters who had Parry could actually guard to penetrate the statue's immunity to normal damage, allowing players to bypass complex mirror puzzles by just waiting in front of statues while blocking.

Platformers

 * In Sly Cooper, the Sympathetic Inspector Antagonist is a fox named Inspector Carmelita Fox who is invulnerable... except in Sly Cooper 3, the Gadgeteer Genius's "Shrink Bomb" works on her, and takes away her infinite HP.
 * Phanto in Super Mario Bros. 2 can be killed by exploiting a glitch. If you have a Toadstool Block (one of those mushroom shaped things you usually need to climb on), you can throw it at the key making it jump in the air. If you do it about a dozen times, the key stops reacting, and instead glows and makes an impact sound. You can then hold the key as long as you like, and Phanto will never show up. You can see it in action here.
 * The Angry Video Game Nerd also found out a way to kill Phanto through a similar glitch. You had to get four cherries, pick four large vegetables, pick the fifth to get a clock to stop time, get another cherry to get an Invincibility Star, and while you're invincible, slam Phanto. However this is a more specific version.

Role-Playing Games

 * At least in the German version of Baldur's Gate, children are supposed to be invincible, possibly out of fear of Media Watchdogs. This can be annoying if they turned hostile to the players for whatever reason. However, if you polymorph them into squirrels by magical spell or wand, you can kill the squirrels - and watch them polymorph back into dead children.
 * Elminster is completely unkillable, even with the game's cheat/debug mode autokill feature on. Drizzt, on the other hand, can actually be killed in a fight, though, in the first game, not a fair one; you could lure him out onto a peninsula in the middle of a lake, then have your characters plink away at him with arrows for twenty minutes or so while he strains vainly in their direction. However, a later patch gave him the ability to go around the lake.
 * In most of of the Ultima single-player RPGs, Lord British is not invulnerable—just very, very, very tough, with limited invulnerability to all but certain weapons. His "death" in Ultima VII, where the player can drop a plaque on his head, was based on a real-life incident where Garriott was injured by a falling metal bar at the Origin offices.
 * this article details all of the ways that Lord British can be turned into a horse and shipped to Nebraska in the Ultima series.
 * In Ultima III, at least, Lord British can be lured outside of his castle (attack him once in his throne room with a ranged weapon, then run)... and then killed with your ship's cannons as easily as they'd kill any other mob.
 * Lord British didn't appear in Ultima VIII: Pagan, but there was Beren, the town sorcerer, who punished any misdeeds the Avatar committed by blowing him up. He couldn't be killed by normal means, but that didn't stop some players from exploiting the game's Super Drowning Skills against him.
 * In Ultima Underworld 2, it is possible, though extremely difficult, to kill NPCs by pushing them into water if there is a body of it available. This can be used to best effect against Dorstag, whom you are supposed to obtain a quest item from through combat or other difficult means. Though most of his plunderable inventory disappears beneath the water with him, the quest item actually stays on the surface for you to pick up. You can kill virtually all npcs by attacking them too, but drowning them avoids retribution.
 * Both Underworld games also have the secret spell Armageddon, which literally kills everyone when it is cast.
 * The exceptions are the inhabitants of Castle British in Underworld 2, including Lord British. They have unlimited health, there isn't any water available, and high-level spells like Armageddon don't work in Brittania because of the blackrock gem encasing the castle.
 * The Elder Scrolls games were notorious for this, especially Morrowind, where everyone and everything was killable. Including plot-requirement NPCs.
 * It is actually possible to finish Morrowind's main quest even if all "plot critical" characters but one are dead, but doing it without being told how in advance requires incredible luck.
 * Fortify Intelligence with Ash Yams. Fortify Health with Vampire Dust. Retrieve Sunder and Keening. Go to Red Mountain. Wield Sunder and Keening bare-handed against Heart of Lorkhan. Win @ Morrowind.
 * Which may have spurred Bethesda to make pretty much every "important" NPC in Oblivion unkillable. If they "die", they drop to the floor unconscious and rise again when the coast is clear. With very little health. And often the coast isn't that clear. Plug-ins remove this invulnerability, as do certain console commands.
 * In some cases, you can simply wait until they're no longer relevant to the plot, in which case they're fair game. Other NPCs never have their 'essential' flags expire.
 * It's also possible to use the Sneak skill to plant an item in their inventory, such as a ring, that does constant damage while worn. They put on the item, and it'll keep their HP at zero even when the "important" flag resurrects them.
 * Dropping them into lava, which always results in an instant reduction to 0 HP, will kill them permanently. Just don't let this happen to Captain Burd.
 * Under normal circumstances, . Except if you use the, making it possible to kill him. He has no death animation, though, so when he dies, he just melts into a weird lump of Dagon-colored goop.
 * Or you can use a weapon enchantment combination of Drain Health 100 and Weakness to Magic 100, each for 6ish seconds, to do over 25500 damage in 8 blows of a melee weapon (100+200+400+800 etc etc), including one blow of 12800 before the 6 seconds of Weakness to Magic runs out. Dagon has 10000 health which regenerates every second. The eighth blow will do just enough to reduce him to a reddish stain on the city floor (literally. He collapses into a puddle).
 * Or you can just hit him until he dies. Takes a while, but totally possible if you yourself are not susceptible to being killed first.
 * The Fallout series is pretty creative with this, even allowing you to passively overdose NPCs with various harmful drugs.
 * You can kill the children who pickpocket you without gaining the Karma title "Child Killer" in the second game by unloading your entire inventory save for armed explosives. That'll show the little bastards.
 * Another way of killing people without "being responsible for it" is to pickpocket THEM and use the interface to move an armed explosive to their inventory, then leave the area and wait. Once you return after waiting long enough, you'll find a dead NPC and nobody's blaming you. Clearly it was a freak case of spontaneous detonation.
 * In Fallout 3 there's even an Achievement/Trophy for doing this, and the game keeps a tally of "Pants Exploded." On the GNR program "The Adventures of Herbert Dashwood," Argyle calls this technique "the ol' Shady Sands Shuffle."
 * That same game, however, follows the same "essential NPC" rules as Oblivion—plot-critical characters do not die (and, since this is a Fallout title, they must and do have protection from possible dismemberment). Children cannot be targeted at all; they have no collision detection for attacks, melee or ranged, and they can't be targeted in VATS mode.
 * In Fallout: New Vegas however, while children remain invulnerable any other NPC can be killed no matter how important they are with the exception of Victor and Yes Man, the excuse being that as AIs they can simply Body Surf to another Securitron unit. Companions are also immortal unless Hardcore Mode is activated.
 * The Overseer in the original Fallout is the only character you can't kill (in a game where you can kill everyone in the entire game,) as he has infinite health and will kill you in one hit...until at the end of the game, when he finally steps out of his death chair and becomes vulnerable (in fact, if you have the Bloody Mess trait, the Berserker title, or have low karma, you'll kill the Overseer automatically.)
 * In Fable, your weapons are taken away from you in Bowerstone, which is merely cosmetic because you can't beat anyone to death there, either (naturally, that's where the game puts all the children). Unfortunately for the people of Bowerstone, the game is only nerfing your damage, and if you can bring in and subsequently protect a mercenary or two, you can murder your way across town all you like!
 * In addition, you can always pick a fight with the guards and navigate the town in a way that gets the townsfolk killed by friendly fire.
 * And also, one of the simplest mods to make for Fable is one that lets you keep your weapons in Bowerstone, with predictable results.
 * Fable II has so many Lord British-type NPCs, it's not even amusing. Notably, you cannot attack when anywhere near Theresa, and if you find a way to snipe her from range with Skill or Will, she will tell you that your weapons have no effect on her.
 * The game actually does hint that there may be a reason for why she's capable of doing that...
 * Median XL is a Diablo 2 mod that features invulnerable trap-like monsters that kill you instantly when you get near, but don't move. This being Diablo, you can imagine how well that went.
 * Not only that, but players figured out ways to kill monsters that are immune to all elements, monsters that cannot even be targeted (tip: damage reflection) and even monsters that cannot be targeted and are immune to all damage and do not have any attack that would trigger damage reflection. There are even four different ways to do so: resurrect monsters with "burn" damage which bypasses resistances and attacks hit points directly; find the item that summons instakill reanimates on your side when you kill enemies; find the item that summons a certain boss whose death animation is coded to autokill nearby monsters on your side and let it "expire"; or use a bugged passive in combination with Open Wounds to cause the monster to take physical damage despite being immune to it.
 * In Torneko: The Last Hope: there are priests in Toro Ruins, and they are treated like monsters, except you can't attack them directly. But you can shoot arrows, magic thunders, or even turn them into items. When this occurs, though, a message appears and says: "Divine retribution!" and a giant lightning bolt drops your HP to 1. Oddly, this is recorded on your adventure log.
 * Kingdom of Loathing had a rumour/legend that the Hermit NPC was killable, via some sort of trickery. As a browser-based not-so-multiplayer role-playing game, he has no stats and no way to be encountered as an enemy. He's said to 'drop' most non-obtainable (or even nonexistent) items in the game.
 * The final boss of Kingdom of Loathing is the Naughty Sorceress, who is supposed to be killable only with a certain item in the inventory. Two players, Cobain Dougans and DarthDud, managed to beat her without the special item and were rewarded with custom Golden Sausage and Silver Sausage items. The description on the Golden Sausage reads, 'Congratulations on your surprising victory, and darn you for forcing us to come up with a way to keep that from ever happening again.'
 * Cobain Dougans has also managed to defeat the Guy Made of Bees, who is also supposed to be unkillable without the use of a certain (different) inventory item.
 * The Sorceress has been beaten a third time by MimiRiceCat. No Bronze Sausage yet, but the Sorceress has been upgraded again. It is now no longer even theoretically possible to kill her without the necessary item—you instantly win if you have it, and instantly lose if you don't.
 * It should be noted that while the others had to get crafty about it, Cobain was one of the highest leveled players in the game, and accomplished this through SHEER FORCE. In a game where the average player ascends by level 15, and there are trophies for those that get to 30, and most clan-quest people hover around 40, he was 116 at the time. Note that leveling up requires you to get a specific base stat (which one depends on your class) up to (current level^2)+ 4, and to get the nth point in a stat requires n^2 total EXP in that stat. Cobain Dougans' screen shot shows that he had a base Mysticality stat of 13354, buffed up to 48476. This means he had over 178.3 million EXP in his Mysticality stat, when the only enemies at the time with a base yield of more than 40 EXP were for seasonal special events. Determinator indeed.
 * It's worth noting that KoL has no policy against botting and no real technical measures against it.
 * To be fair, the limits placed on adventures and consumption each day do restrict how effective botting is in regard to leveling, so long as the multi-account policies are followed.
 * In the last level of Nethack, a player will meet the Riders, three immortal beings who, when killed, will always rise from the dead again. There are only two known ways to dispose of them permanently: kill them, and fill the level entirely with monsters so they have nowhere to reappear, or turn them into green slime. Neither is considered a bug, although most players consider them much more of a hassle than simply finishing the game.
 * Amusingly, it's also possible to level-drain two of the three until they become weak enough to enslave with Charm Monster. Now you're playing with power!
 * Some players like to take this to the next level, and kill entire species. This is easy for most monsters, as almost any monster that is created 120 times is considered extinct by the game, and will never be randomly generated again. You'd think this wouldn't apply to unique monsters—by definition, they are created only once, yes? But in fact, a monster that is brought back somehow counts as a new monster for extinction purposes. Stoning and unstoning a monster counts. For monsters that resist stoning, a wand of undead turning will resurrect the monster. For those few stone-resistant monsters that leave no corpse, an Amulet of Life Saving will also increase the extinction counter. But there is one monster, Juiblex, who is unique, stone-resistant, leaves no corpse, and will never pick up an amulet, and thus cannot be made extinct. But even he can be killed again, just the one extra time, if he randomly spawned with the amulet in his inventory.
 * In earlier versions, it was possible to tin Death. Eating him had the expected result. (With the bonus of having a Hall of Fame scoring: approximately, "Died by eating Death".
 * Nethack also gives us the Mail Daemon, who appears and disappears within the span of one turn and, therefore, can't normally be interacted with at all, much less killed. So, naturally, sufficiently Crazy Prepared players have found a way to kill it, preventing further messages from being delivered; to do this, the player needs to.
 * The first Valkyrie Profile game has Brahms, Lord of Vampires. You are not supposed to beat him. If you do through luck, Level Grinding, or cheating, the game just deposits you back into the Overworld without ever mentioning it again, and the game pretends that you had chosen the "don't fight him" option. He appears again in the Bonus Dungeon, but by that time you are expected to be strong enough to match him.
 * In the original NES version of Final Fantasy III, you have what is supposed to be a Hopeless Boss Fight against Bahamut early in the game. He has 65535 Hit Points (an absurd number for that game), and fully heals every single round, but it is still possible to kill him. If you do, not only do you get no reward, but you get punished—it becomes impossible to get him as a summon later in the game.
 * Note that 65535 is obviously 2^16-1, and so is likely the maximum possible health the technical limits would allow the devs to give him.
 * Also note that PC damage is capped at 9999, and the party limit is 4. At that point, it's quite impossible to deal more than 39996 damage in a round, then he full-heals. (In reality, that 39996 is more akin to, say, 400.)
 * In EarthBound, Giygas is supposed to be killable through one means and one means only: Paula's "Pray" command. While he does have a "real" HP value, calculational trickery otherwise keeps him alive. However, in the Game Boy Advance Compilation Rerelease, using a Viper on Giygas can poison him... and the poison will eventually kill him. On the other hand, since the battle wasn't ended the scripted way, glitchery ensues and you end up in a world preconfigured for the game's ending... an ending which won't happen now.
 * Master Belch is immune to damage of any kind until you use the Fly Honey on him. However, the Hungry HP-Sucker doesn't count as damage, because it's a draining effect. It's possible to kill him the long way by exploiting his vulnerability to status effects and drawing his hit points out the long way.
 * In Mother 3, the only way to kill the Bonus Boss Pig King Statue is supposed to be with either a lucky shot of PK Flash, or use the New Year's Eve Bomb. He has 100 million HP otherwise, and regularly hits you for more HP than you probably have. It's just not possible to beat him conventionally without cheat codes, if only because, at the end of the day, long after you've run out of PP and healing items, he still has 99,000,000 HP left to go. It's a numbers game and his are just far, far, far superior to yours. That hasn't stopped people from trying, though. Problem is, for the people strong enough to go the distance, it turns out he has another dirty trick: freezing the game. He hadn't even worn down all 99,999,999 HP—according to a comment, it was somewhere around 2 million.
 * Secret of Mana has Charon, the guide who takes you to the Moon Palace, who is actually just a common enemy called a Robin Foot locked into a position where he cannot attack the player. He can't be hit with weapons, but magic can kill poor Charon. Additionally, the final boss is supposed to only be damaged under very specific circumstances, but his defenses are not impenetrable to normal weapons when charged to sufficient levels.
 * Disgaea has another example of this. NPCs are everywhere across the castle - Running the hospital, the shops, even the portal that takes you to the storyline maps. Now, you can't attack them in the castle.... or can you? (Here's a hint: You can.) All you have to do is call an assembly. If one of the NPCs shows up, you can happily beat the tar out of them. Then when you get back to the castle, you'll find a little gravestone where they were. Wait a minute.... you just killed the demon running the Hospital... how are you supposed to heal? Just save, reset, and they'll be back in their spots again.
 * The series also features a few Hopeless Boss Fights that you must lose to advance the plot (Etna and Laharl in Disgaea 2, for instance). These enemies are never truly invincible, just way more powerful than your party is expected to be. This being Disgaea, you can stop and level grind for ages until you are capable of winning. Typically results in a Nonstandard Game Over. Since seeing all the different endings is a frequent goal of players, plenty of people actually do this.
 * Most of the townsfolk that aren't important in some way or merchants can be killed in Final Fantasy Adventure if you have the patience to do so.
 * It's actually possible to kill Fargus in Fire Emblem: The Blazing Sword. You're warned not to do so because it's a Hopeless Boss Fight otherwise, but people have managed to defeat him legitimately. Alas, it's not a good idea to do this because this causes a game over just for attacking him.
 * In Geneology of the Holy War, the Final Boss appears on the map in Chapter 10. This is supposed to be a Hopeless Boss Fight, but you actually can Cherry Tap or if you're lucky, Holsety them to death. If you manage to do this, the boss even says "Playtime is over - I'm going home."
 * Almost the exact same instance occurs in Radiant Dawn, possibly making it a Shout-Out - the Big Bad appears in chapter 4-3 amongst his hordes of Mooks. He's supposed to flee once a certain ally appears during the battle, but it's possible to get to him and take him out first. As above, he makes a pompous exit and returns later in the story no worse for the wear.
 * Evil Islands has many monsters that were designed as unkillable by giving them tons of HP and rapid regeneration. However, with the introduction of easy mode in a patch, most of them became technically possible to kill, even though the process was long, difficult, and involved a share of luck. Enthusiasts posted a detailed guide to killing every single creature outside of towns, except two dragons that are too tough to kill even this way and a frog in the tutorial, which only survives because the player has no ranged weapons at this point. This slaughter, nicknamed "Project Genocide", completely breaks the game scripts, making quests play in the wrong order, NPCs making references to future events, and corpses and empty spaces participating in conversations.
 * Monster Girl Quest Paradox has Reaper as an optional boss in the first chapter. She was supposed to be unbeatable until later chapters, due to the level cap and other limitations. Players managed to kill her, which led the creators to release the Labyrinth of Chaos, an infinite Bonus Dungeon originally meant for the third chapter. Getting as far as possible in the Labyrinth is now the new hobby for serious players, and some have managed to defeat Reaper in the Labyrinth.

Tabletop Games

 * An old adage in tabletop RPGs, and similar to this trope, is "If you stat it, they will kill it." This is probably a take-off of the Predator quote, "If it bleeds, we can kill it."
 * This may be why various RPGs avoid statting certain characters. For instance, Spirit of the Century gives only a few ballpark skills for Dr. Methusala, but only as a last resort. GMs are encouraged to treat him as an event, rather than a character.
 * Aberrant gives only a partial set of stats, and those largely being estimated values, for Divis Mal and Caestus Pax for precisely the same reason. (And what stats you do have are so ridiculously high that unless you're playing with vastly-more-powerful-than-average PCs, you're not so much as mussing their hair.)
 * Similarly, the tongue-in-cheek First Law of Munchkinism: "Any finite number can be reduced to zero."
 * The first edition of Dungeons & Dragons gave the gods stats. This led a lot of players to treat them just like really tough monsters and try to kill them. Later editions generally avoided statting the gods themselves, and if they needed to make a personal appearance, would send an avatar with a fraction of their powers (but still really tough).
 * The 3rd ed book Deities and Demigods contained almost exclusively stats and info on most gods in the game, including the Faerunian pantheon and the Greek, Norse and Egyptian pantheons. A majority of them are grossly underpowered and badly built, ripe for having player parties kill them and steal their divine powers unless the DM enforces the special rules for deities.
 * The Planescape entity known as the Lady of Pain has no stats for this very reason. The fans wouldn't have it any other way, to the degree that when the 3rd edition Planar Handbook statted her Character Alignment and nothing else it was met with disapproval.
 * In the online novel "Fire and Dust", the villain is convinced her gamebreaking macguffin will allow her to defeat even the Lady,.
 * Writers for the Ravenloft setting split the difference with Gwydion, an Eldritch Abomination: they wrote up stats for his tentacles, but never give the heroes a chance to confront his actual, unstatted body.
 * A fourth Edition Ritual called Loremaster's Bargain grants you an audience with one being with information that you need, often a deity or extraplanar being. Part of the ritual description states that they cannot be attacked or physically interacted with.
 * In a variation, the Tarrasque is designed to be the most powerful monster in the game - it's huge, it's strong, and it regenerates any damage quickly. Theoretically, you could beat it, but the rules are stacked against you, so players gave always been trying to come up with creative ways to fight it. One thread on rpg.net described how the rules make it entirely possible to have a city capture the Tarrasque and use it as a neverending supply of food, since it'll always regrow what it loses.
 * On the non-D&D front, the crew at Pinnacle would recite the adage about statting things in the first edition of the Deadlands books. They would refuse to stat certain characters in order to railroad people into sticking with the metaplot. Seems to have been reversed in the Reloaded release, though.
 * Stone in Deadlands has no stats for this exact reason.
 * The Shadowrun module "Harlequin" refuses to stat the title elf, and explicitly calls this out as the reason. (Great Dragons, meanwhile, avert the Postulate not by not having stats, but by having a mechanic in their stats that allows them to say The Battle Didn't Count, to appear dead but actually survive, and then destroy the PC party via manipulation from a place of complete safety.
 * One of the Shadowrun developers used to recount an incident when a fan described how his party had setoff a Briefcase Nuke the moment they met Harlequin, sacrificing themselves to kill the unkillable. Their GM had let it work because "there was no way even Harlequin would be walking around with a custom anti-nuke protection spell". The developer responded that he would have ruled that knowing Humanity the way he did & being the kind of guy he was, Harlequin would have dropped everything to create an anti-nuke protection spell about 10 min after the first test in 1945 & would not have let it lapse since then.
 * In 1st edition he wouldn't even have needed a custom spell. Blast Barrier was an absolute effect... if you had it up, explosions of any magnitude wouldn't touch you. This is why they got rid of Barrier spells.
 * As of late 4th edition Harlequin has stats, and is officially killable (even if it would still be difficult). This is justified in-setting as him having gone through a grueling event that stripped him of most of his power, bringing him down to (mostly) mortal.
 * One Vampire: The Masquerade book has a section called "Rules for Fighting Caine", the first vampire, specifically for this purpose. It consists of the two words "You lose."
 * The third edition of the book made sure to give all vampires of third generation and below at least one Plot Device power to keep the players from just killing them willy nilly.
 * Which is amusingly inverted in the Time of Judgement, which has a couple of scenarios that go out of their way to give players ways to kill (or help kill) 3rd generation vampires (and Cain!) willy nilly.
 * The same "rules" are used in the LotR RPG to describe fighting Sauron.
 * The older MERP gave statistics for him in the Necromancer of Dol Guldur supplement. He's immensely powerful at 240th level (for comparison, Nazgul are 20th level in the original book or 40th in the supplements and Gandalf et al are 60th level), but since MERP has open ended rolls and instant-death criticals, even the lowliest hero could get lucky and kill him with a lucky combination of 96-100 attack rolls and a decent critical hit, assuming they could get into combat with him in the first place.
 * Similarly, in Call of Cthulhu (tabletop game), the first of the combat abilities of Cthulhu reads: "Each round 1D3 investigators are scooped up in Cthulhu's flabby claws to die hideously". (Through Memetic Mutation, or perhaps from an earlier edition, this often gets quoted as "Cthulhu devours 1d6 investigators per round" or the like.)
 * Early editions had Cthulhu eating 1d4 PLAYERS a round.
 * Just seeing Cthulhu forces a character to lose 1d100 SAN (sanity). The maximum SAN is 100. Do the math.
 * Though the thing that makes him this trope is what happens if you do kill Cthulhu. He reforms a few minutes later, fully recovered. Nuke him and he comes back radioactive.
 * Rifts being Rifts, when it added "Pantheons of the Megaverse", the first thing many players tried to do was take on Odin, Ra, Marduk, or whoever was handy. But the book also described beings far more powerful with lines as succinct as "tick them off and it's time to roll up new characters." No stats or names were provided, but presumably the writers were referring to capital-G God and distinguishing Him from those wannabes on Olympus. (It also suggested that Game Masters didn't including Him in the campaign, since constant divine intervention makes the game kind of boring.)
 * 7th Sea has one of its most infamous villains, Captain Reis, on the cover. He has stats. He's also nearly impossible to hit... with a sword. However, he doesn't wear armor and you can't block bullets. Shoot him and throw in all your drama dice and you can put a hole in his skull.
 * In GURPS, it is impossible to kill anything with Unkillable 2 or 3. However, even if the GM gives an NPC one of these traits, player can still attempt to do any number of other nasty things to it, like mind controlling it or chopping off its arms, which kind of exemplifies this trope.
 * In GURPS, it is impossible to kill anything with Unkillable 2 or 3. However, even if the GM gives an NPC one of these traits, player can still attempt to do any number of other nasty things to it, like mind controlling it or chopping off its arms, which kind of exemplifies this trope.

Webcomics

 * In the webcomic Kid Radd (which plays with and lampshades a number of videogame tropes) the final boss of the game Mofo was supposed to be only vulnerable to a special ability none of the characters had. It turned out that he just had a lot of hit points and regenerated them each turn, which allowed the team to defeat him.
 * In an in-universe nod to the Postulate, this unlocks a tongue-in-cheek ending to the game where they are chided for "cheating".
 * Said game was a Lawyer-Friendly Cameo of EarthBound, and as discussed above, Giygas has similar protection.
 * In Homestuck, the leader of criminal gang The Felt is named Lord English, after a particular spin put on a cue ball in pool. Creator Andrew Hussie hadn't even heard about Lord British until later and, when he was informed about similarity between the names, decided to make Lord English a Lord British Postulate, mentioning in a character's narration that he can only be killed by exploiting "numerous bugs and glitches in spacetime."
 * This particular Retcon surprisingly fits very well within the Time Travel-related powers that the rest of The Felt possess.
 * Eridan's NPCs in the Land of Wrath and Angels were supposed to be unkillable, but Eridan believed they were enemies and somehow managed to kill them all through sheer determination. Sheer determination and about a minute apiece of sustained fire from Ahab's Crosshairs.
 * Unfortunately, after too much of this, they became hostile and actually did begin attacking him; how he managed to fight off and eventually kill the entire species is a mystery not explored by the comic.

Other

 * Dwarf Fortress players will do their best to kill anything, and have even gone so far as to survive digging too deep by . Other examples include draining an entire ocean to trap walruses, digging out undiggable stone, and, in a previous version, annihilating all the Hidden Fun Stuff and . This last is probably the reason why the new version's HFS is so much worse.
 * Back in the 2D era, the Hidden Fun Stuff automatically killed you in just a short time after you mined the first cotton candy ore. The 3D version remedied that problem. Now you can exploit this trope to the max.
 * Toady's stated design intent to make it possible to annihilate all life on a generated world, ushering in the Age of Emptiness, makes this the most complete aversion. (Versions 31.16-.18 have made this impossible, but may become doable under later implemented conditions.)
 * In an unusual case of a strategy game, Command & Conquer Tiberian Sun: Firestorm has two of those. The CABAL Core Defender (a boss actually) who should be unbeatable except when abusing his Super Drowning Skills or using stealthed One-Hit Kill capable WALLS and the super-charged veinhole monster from a GDI mission, which will die when you fire long enough on it. ("Long enough" being a long time.)
 * Alter Aeon seems to enjoy tormenting players with this: in the starting city, there is an NPC called "The Captain of the Guard". The message for the area explicitly tells the player (paraphrased) "This is the Captain of the Guard. He cannot be killed. No matter how many players you bring, you will not kill him". Naturally, many see this as a challenge.
 * In The Legend of Zelda: Link's Awakening, chicke... er, Cuccos and dogs can't be killed with the sword, attacking the former enough causes a whole flock of Cuccos to start swarming Link (as is the norm in Zelda games), and attacking the latter triggers a counterattack. Use the Fire Rod or Magic Powder, however, and not only can you kill them, but an active Cucco swarm will stop. (There's loyalty for you!)
 * Metroid Zero Mission: During your steath escape through Chozodia, you'll spot a Power Bomb Tank held by a statue in a spot just above the room you're in. A few seconds later, you get there to find it gone, and a Space Pirate a couple screens up above is absconding with the prize. Sadly, not even tool-assisted speedrunners are capable of catching up with him.
 * Immortal Defense has a boss at the end of the second campaign who's supposed to be a Hopeless Boss Fight, but players who are just that good have gotten him. The developer didn't think anyone would be able to do it and the game assumes the normal events happened where the boss wins and continues from there. The rest of the game, heavily psychological, goes on to make near-record amounts of no sense.
 * In Age of Mythology: The Titans expansion, one level has you scrambling to revive a giant Guardian statue in Egypt, because an equally giant Titan (Cerberus) is coming who is designed such that killing him should only be realistically possible using this guardian, due to his massive damage and hp. However, using vast number of priests, who gain damage bonuses towards creatures of Myth, it is quite possible to kill him without awakening the guardian, though he does tend to kill a lot of them before he goes down.
 * One of the missions of Necropolis scenario in Heroes of Might and Magic V: Tribes of the East features a fortified Orc town with a huge army. This army never leaves the town, and the game specifically warns you that you don't have to and shouldn't attack it. However, it is possible to destroy it, by prudent use of Dark magic (specifically, Berserk and Puppet Master spells).
 * Cap'n Hector from the Escape Velocity games was an NPC who would remind players to register (pay for) the shareware game. After the 30 day trial period ended, the Cap'n would start warping in to attack your starship every chance she got, usually resulting in a very quick death. However, while Hector was invincible to conventional attack, it was possible to kill or disable her with splash damage in the original game.
 * An the first Assassins Creed, it is possible to kill the guards on higher up areas by simply using gentle push on them until they fall off the ledge. They then proceed to die from fall damage.
 * And it is hilarious.