Too Powerful to Live

A villain who is just too powerful to exist for more than an episode or two. If they aren't killed now, their presence will dominate the entire story forever.

If the writers try re-using them, the result is almost always Villain Decay.

One noted tendency of these characters is establishing their power by laying the smack down on the incumbent main villain, emphasizing just how dire a threat they are. Less commonly, rather than a new villain come to town it can be the main villain who gets a power boost, which if not explicitly temporary is then quickly destroyed or discarded before they can truly exploit it.

A villainous version of Deus Exit Machina. The heroic version of this trope is Too Cool to Live. See also How to Stop the Deus Ex Machina. Compare Too Happy to Live and Too Cool to Live.

Anime & Manga

 * Shabranigdo from The Slayers.
 * from Death Note died quickly because the Oba realized had they lived, Light wouldn't have been such a threat,
 * Sabrac of Shakugan no Shana shows up for a single epic battle in the second season before disappearing again. Luckily for the heroes, the Badass Psycho for Hire has no interest in the final battle after accomplishing his task.
 * Max Kaien from The Five Star Stories, while isn't actually a villain, is definitely too overpowered to let him roam freely. So after being allowed a run as a Game Breaker in his home world, he was rather quickly Put on a Bus and shipped into the Alternate Universe, where's he's came out as somewhat more balanced.
 * Mariko in Elfen Lied is by far the strongest character in the story when she's introduced, that's why she has bombs implanted everywhere in her body, that will detonate if a code is not transmitted every thirty minutes..
 * Broly from Dragon Ball Z, who infinitely gets stronger as long as he is alive (if he doesn't have a Power Limiter binding him), so he absolutely had to be killed quickly or everything would be doomed. It doesn't help that he is a completely and utterly insane lunatic whose only desire is to destroy everything around him, especially Goku.
 * His power is maximum.
 * from Katanagatari is literally Too Powerful to Live.
 * Reinforce/The Darkness of the Book of Darkness from Magical Girl Lyrical Nanoha As, an Eldritch Abomination Omnicidal Maniac capable of destroying worlds and in the form of Reinforce, easily the most powerful mage that ever appeared in the franchise. Naturally, once it appeared, it quickly became the only main villain in the series who is made Deader Than Dead with no chance of survival, which sadly includes poor Reinforce.
 * Sara from Samurai Champloo. She's easily the second strongest character in the series, giving both Mugen and Jin a run for their money.
 * The Chimera Ant King Meryem from Hunter X Hunter, along with his Royal Guard. They were easily the most powerful beings in the world, and none of the human Hunters sent against them could beat them in a fair fight. So they don't fight fair.

Comic Books

 * Doomsday was pretty much the original example: his entire purpose was pretty much to kill Superman, so the writers could spend several plot arcs dealing with a post-Superman world.
 * The Authority encounters this type of villain fairly frequently. Their usual response is to kill said villain after a huge epic battle, since if they were allowed to live they'd endanger millions.
 * This is why the Big Bads of most comic Crisis Crossovers die by the end of the story. If they do reappear as dead characters are wont to do in comics, they usually show up years later and rarely at that. The villains of DCU "Crisis" crossovers are especially notorious examples and suffer pretty spectacular deaths:
 * The Anti Monitor, the Big Bad of Crisis on Infinite Earths. A cosmic superbeing who used his powers over antimatter to destroy the Multiverse. In the end he was blasted with positive matter, Darkseid's Omega Beams, and was punched into a sun by Superman. He didn't return until decades later in real time, when the Multiverse was reconstructed. And at the end of that crossover, an entire planet blew up in his face and he got punched by Superboy Prime halfway across the galaxy.
 * Alexander Luthor Jr., the Big Bad of Infinite Crisis. He was essentially a superpowered Lex Luthor . After a year of flawlessly manipulating the heroes and villains of the DCU (getting rather close to Villain Sue status at times), he nearly destroyed the current universe to create his own "perfect" Earth. In the end he was completely defeated and was brutally murdered in a filthy alley by the Joker.
 * After years of sitting on his throne and slowly decaying, Darkseid finally crossed this threshold in Final Crisis. The Anti-Life Equation granted Darkseid absolute control over all. And his very existence destabilized the fabric of space/time; essentially dragging all reality with him to his inevitable death. In the end he got shot with an anti New God bullet (By Batman, one of the staunchest defenders of the One Rule), had his soul taken away by the New Gods' psychopomp the Black Racer, and had his consciousness shattered by Superman's singing.
 * The other big villain of Final Crisis, Mandrakk the Dark Monitor, didn't survive the end of the story either.
 * The Sun-Eater in Final Night. It's not a villain so much as a force of nature.
 * Phoenix, especially once they decided it was not a separate entity from Jean Grey.
 * One-shot villains in Doctor Strange stories tend to be beings so absurdly powerful that Strange can't even fight them, let alone defeat them. The best he can do is bluff them into leaving this world alone, convince them Earth isn't worth the bother, strike some sort of bargain, or distract them somehow. Try not to think about how frighteningly impermanent that solution is, nor what would happen if two or three of them decided to try again...

Film
"Megatron: Nobody summons Megatron... Unicron:"
 * Unicron, from Transformers - more specifically, The Movie. He appears without any explanation, shakes up the status quo with a great deal of damage and destruction, and is finally polite enough to go boom at the end of the movie. One of the film's highlights comes when he asserts his authority over an already-dying Megatron:


 * However, his floating head was apparently still alive as a new moon for Cybertron, and it tried to get Starscream's ghost to resurrect its body.

Literature

 * Professor Moriarty from Sherlock Holmes is a good example of this. It's implied that Holmes has been fighting him for years, but he dies at the end of the story that introduces him and is only referred to in two later stories.
 * Of course, he was supposed to have killed Holmes too. Were it not for the fan outcry that would have been the last Sherlock Holmes story.

Live Action TV

 * The Chairman from Walker, Texas Ranger may qualify. He is the head villain - played by Michael Ironside, no less - for a full four-episode Story Arc, puts Walker and his loved ones through the ordeal of their lives, then dies and is never heard from again.
 * Species 8472 does this in Star Trek: Voyager, starting things off with a spectacular use of The Worf Effect on the Borg (see below) and forcing the Collective into an Enemy Mine with the heroes.
 * The Borg in their original appearances on Star Trek: The Next Generation, up to the end of "The Best of Both Worlds." After that, the inevitable Villain Decay got them.
 * Plenty of examples appear over the course of Doctor Who's extremely long run, the list of virtually unstoppable Physical Gods the Doctor has defeated and then never mentioned again including Sutekh, Fenric and The Beast.
 * Arthur Petrelli on Heroes.
 * Surprisingly averted by Sylar himself, despite his Villain Sue status as the most powerful living superhuman, as the writers have wisely avoided giving him any outright Game Breaker powers like Matt's mind-control or Hiro's space-time manipulation. He mostly relies on telekinesis, regeneration, lightning blasts, and shapeshifting (with flight recently thrown in) which makes him tough, but not quite a walking automatic I Win button. Indeed while he's proven to be a very skilled fighter many of his powers are geared more towards Super Dickery rather than straight up combat, in keeping with his Wild Card status.
 * There is also a character in one episode who could produce black holes, and while he wasn't ridiculously overpowered, it's made clear that he could kill Sylar in an instant. Bennett tries to get him to do this, but he just sucks himself into a hole instead.
 * In the one-off Babylon 5 Made for TV Movie Thirdspace, the Thirdspace Aliens. Much of their shtick involved influencing the minds of anyone who spent too much time near their Artifact of Doom. Destroying it reversed the effects.

Video Games

 * The Statesman Task Force in City of Heroes is about his nemesis Lord Recluse doing this to himself. When you finally get to confront him, he uses a machine that taps into most of the superheroes in the world (except for your team, conveniently) and becomes way, way stronger than normal. The tricky part is surviving his assault while taking out the machines so he can be brought back down to normal and defeated.
 * Lancer in Fate/stay night. Gaebolg gives him a low-cost, instant-kill, guaranteed-hit ultimate attack, and also inflicts wounds that don't heal as long as his lance still exists. He's also extremely fast, and Irish. You don't mess with the Irish, especially when they're wearing blue spandex. After he shows up, he's immediately put on a bus until 90% of the first two routes, and then Heavens Feel drops a bridge on him. The two times he did get to use the attack, his targets pulled out hax of their own to just narrowly avoid a fatality anyway. To be fair, he was under explicit orders to not fight any battles to the death.
 * It's generally held that, if he had, they would have easily won the war.

Web Original
"Seto Kaiba: These new cards I won from Pegasus are incredible. In fact, they're so incredible that I will never use them again!"
 * Yu-Gi-Oh the Abridged Series of course parodied this trope in "The Abridged Movie":

Western Animation

 * Murko fills this role on Birdman, invoking The Worf Effect on Pentagon security, F.E.A.R., and finally Falcon Seven before facing Birdman in battle. Suffice to say, he lives up to the hype, coming as close as the series ever got to Nightmare Fuel.
 * The various The Virus plus Reality Warper combos from Codename: Kids Next Door, like Madam Margaret and Grandfather.
 * Mumm-Ra in Thundercats once discovered an Artifact of Doom that quadrupled his powers. He was laying the smackdown on the Thundercats with it, but when he needed to return to his pyramid to rest the Ancient Spirits Of Evil denied him entrance. They were jealous and fearful that with the orb, Mumm-Ra would forsake them, so they forced him to ditch it. And they still complain that he loses to Lion-O.
 * Ben 10's arch-enemy Vilgax was the Big Bad of the show's first season. To stop him from dominating the remaining three seasons, he was conveniently Sent To Another Dimension at the end of each of his subsequent appearances (usually 1 per season) so the characters won't have to worry about him.
 * There is also the Giant Space Tick From Nowhere in the episode that introduced Cannonbolt. Within a few hours, it came close to causing The End of the World as We Know It, with nothing Ben had being unable to even scratch its exoskeleton. He crashes into it with Cannonbolt, status quo returns, and it is never heard from again.
 * Pariah Dark does this in the first Danny Phantom movie, "Reign Storm," stomping Vlad Plasmius and darn near conquering Earth before he is put back in his box. The same applies to Evil Counterpart Dark Danny.
 * The Liquidator from Darkwing Duck was basically the most powerful enemy DW ever encountered, being nearly impossible to catch, invulnerable to to physical strikes, and able to control all the water in St. Canard. He only finally stopped when Darkwing dosed him with quick drying cement. Because of this (as well as the fact his dialogue was difficult to write), he was from then on only seen along side the hero's four other greatest enemies to make him easier to defeat.
 * The Nameless One (no, not that one), Dungeons and Dragons- apparently The Man Behind the Man to Venger, but this does not stop him giving everyone's favorite one-horned force of evil a good working-over. Unusually, he does not die at the end after his episode of terror. Instead, he winds up leaving the characters (and the audience) in suspense over his probable return, and proceeds to never appear again.
 * Gigabyte in Re Boot was only around for one episode. He was a fusion of Megabyte and Hexadecimal (or the original form if you count the Retcon). He had Megabyte's strength, would have had Hexadecimal's powers if she hadn't been drained of energy at the time of fusion, and could Absorb Energy, which gradually unlocked Hexadecimal's powers. The only way to stop him for good was to re-separate him back into Megabyte and Hexadecimal, which is why he never appeared again outside of flashbacks.
 * Trigon the Terrible on Teen Titans invades earth and turns it into a literal hell before he's banished (and possibly killed) and his magic undone by his daughter, Raven. The series would have concluded with his defeat—but they got extended for another season.
 * Tigerhawk of Beast Wars. His first appearance had him  The next episode he was killed taking on a powerful warship buying time for the Maximals.
 * Amazo in Justice League. His initial motivation is killed when he aquires telepathy from Martian Manhunter and realizes he's being manipulated by Lex Luthor. He realizes all this is beneath him and goes out into the universe in search of meaning. He returns in the Unlimited series showing himself to be even more this trope plowing through battalions of superheroes but leaves again searching for meaning.
 * Nightmare Moon, Discord and Queen Chrysalis from My Little Pony Friendship Is Magic. All three effectively win with their mere appearance (Nightmare Moon and Chrysalis imprison Celestia with ease, while Discord instantly negates the one thing that can defeat him), meaning they had to be dealt with immediately lest the series end on a downer.