Self-Disposing Villain

The Monster of the Week has the decency to be sufficiently inhuman, faceless and irredeemably evil that the heroes feel no guilt over slaying them. So polite! But their human masters, and human villains in general, don't extend the same courtesy.

What exactly is a hero supposed to do once he catches an evil human sorcerer? Killing is right out, but letting them go free is bound to cause more mayhem. The other options aren't much better: Does he explain to the police that he was stealing chunks of soul from Innocent Bystanders, cursing them to horrific nightmares, followed by death? Even if the police are part of The Masquerade and can get the sorcerer jailed for other charges, what prison could hold him? Big Damn Villains or Always a Bigger Fish aren't always around when you need them. And very often the hero can't count on a Chosen Many Corps or The Men in Black to back him up with high tech/mystical imprisonment. The hero may have his powers lost/stolen every other episode, but permanently Depowering a villain is rarely ever possible for an unsympathetic villain. And let's not even get into Brainwashing for the Greater Good.

But if the hero kills the sorcerer, he will be just like him.

What exactly is a hero to do?

Thankfully, villains tend not to realize this or exploit it. Instead of begging for mercy and "playing nice" for a few episodes, they go for broke. The villain hanging on the cliffside will accept the offered hand and Last Second Chance, only to try and backstab the hero, making his self-defense kill morally just. Or better for the hero's conscience, the villain will scream "No! This Cannot Be!! I just need more power!!!" Cue the Superpower Meltdown that destroys the Artifact of Doom empowering him. In essence, their excessive ego and poor planning somehow gets them Hoist By Their Own Petard, put in a Fate Worse Than Death, or destroyed by their own creation/plan. Less lethally, they may dispose of themselves in a non-threatening form, like in ending up in a Convenient Coma, as an amnesiac, Depowered, or trapped in a Tailor-Made Prison.

The purpose of this trope is to allow the hero to continue to be a no-kill hero without having to worry about the morally complex minutia of disposing of a human adversary. This often happens in series aimed at children where killing is wildly inappropriate for the target audience or tone of the setting, and in more adult fare when the hero being presented is a Knight in Shining Armor, so sullying him with Grey and Grey Morality problems would tarnish his image.

This easy cleanup also extends to having the hero's secret identity protected if the villain discovers it. Expect the aftereffects of the Phlebotinum they were using (or even a simple Tap on the Head) to give them Laser-Guided Amnesia. At times, it even makes them forget they were a villain.

This can work so well that the hero can now walk away from this climactic fight into a Burger Fool and order a Delicious Extra Meaty without feeling the tiniest shred of guilt. Well, except maybe for the empty calories in the fries, and if they're really Nice Guys that the villain got himself killed/trapped/disposed off. But whatever. It's not like he'll be back next episode anyway.

Compare Disney Villain Death, which similarly disposes of a villain for good while leaving the hero's hands clean. If you are looking for a trope about disposing of a body rather than disposing of a threat, see No Body Left Behind instead.

Anime and Manga

 * Johan Liebert of Monster holds a boy hostage and forces Tenma to make the Sadistic Choice of killing him or letting the boy die. Then the boy's father conveniently shows up armed and suddenly it's a moot point.
 * Sailor Moon: The major villains (Quirky Miniboss Squad and up) have a tendency to either kill each other off for various reasons (You Have Failed Me, You Have Outlived Your Usefulness, Evil Versus Evil) or be destroyed by their own technology/attacks, leaving the less human looking Monsters of the Week and Big Bads to be destroyed by the heroes. This is especially true of the Witches 5 from the S season. Eudial is killed by Mimette, Mimette is killed by Tellu, Tellu is killed by her own plant, Viluy is killed by her own nanobots, and Cyprine and Ptilol actually end up killing each other in battle. The Sailor Senshi never have to do a thing.
 * Note that this is only in the anime; in the manga, the Senshi had no qualms about killing the human/human like villains.

Comic Books

 * The Composite Superman, a Silver Age enemy of Superman and Batman, possessed all the powers of the Legion of Super-Heroes and knowledge of the heroes' secret identities. He defeated them and demanded that they give up being heroes, and they actually considered it(!), but the powers then faded away, leaving him without even the memories of ever having been a villain! (This actually happened *twice*!)
 * The Marvel Universe gives us Thanos, who routinely comes dangerously close to complete universal domination, only to screw up in some fashion at the last moment and engineer his own defeat. This behavior is noted by both Vision and Adam Warlock in The Infinity Gauntlet, wherein he decides to become intangible, accidentally allowing his alledged granddaughter to simply grab the titular Cosmic Keystone from his body with no resistance at all. Adam Warlock then talked Thanos into making a temporary Heel Face Turn with a Hannibal Lecture that amounted to, "Face it. You've had omnipotence twice now and blown it both times. Do you really think it was by accident?"

Film

 * All of the Batman films since 1989 used this trope extensively, at least regarding named villains. Batman and Robin (and later Batgirl) never, ever kill. Their opponents are beaten by falling to their deaths trying to kill the heroes (Two Face), killed by another villain (Schreck and The Penguin by Catwoman) driven insane from overdosing on Phlebotinum (Riddler), and captured in Tailor Made Prisons (Mr. Freeze, Poison Ivy). The only one who dies (mostly) by Batman's hand is the Two Face from The Dark Knight Saga. Stretched a bit in Batman Begins, where Batman refuses to deliver a killing blow to Ra's al Ghul but nonetheless leaves him to die as the derailed train on which they're riding crashes.
 * Which is completely at odds with his usual going-all-out-to-save-everybody character. Batman could also be considered to be responsible for Two-Face's Death in Batman Forever, as he knew exactly what he was doing when he flung those coins.
 * He knew Two Face would be unable to make his decision with his coin now piled with all the others, and possibly even the Villainous Breakdown following it, but maybe not he would slip and fall. Granted however he doesn't save him either (it should perhaps be noted that he advised against Robin killing Two Face out of revenge, explaining cryptically how his own previous murders of villains had granted him little resolution and peace. It is possible, since his life already skewed, he took this blow so Robin wouldn't have to).
 * In Batman Begins it's justified since Batman is only shaping his philosophy, and Ra's would probably have been capable of saving himself, but chose death instead of getting humiliated by being captured alive. As opposed to the Tim Burton movies where Bats is several times seen casually murdering Mooks with impunity.
 * Also in the original 1989 Batman, the Joker also falls to his death in a botched escape attempt (Batman ropes his leg to a gargoyle, however Joker ignores it and continues trying to climb up the ladder of his escape helicopter, unlatching the gargoyle that ultimately drags him down). Of course, given Batman's intense grudge against Joker for  it is left ambiguous whether he would have spared his life had this not happened, especially since he seemingly slugged him out of a window ledge just moments prior.
 * Of course, Batman couldn't be expected to know the gargoyle was so weak that it would give way as soon as any pressure was put on it - Joker should have lost his grip and dangled from the gargoyle, not pulled it loose. In fact, gravity by itself should have held it in place against Joker's grip.
 * Used in all three Spider-Man movies to remove the villain while allowing the main character to keep to his code against killing. The first Green Goblin is Hoist by His Own Petard, Dr. Octopus and the second Goblin die due to Redemption Equals Death, and Eddie Brock kills himself by diving into the Venom symbiote just as Spidey's about to incinerate it.
 * In the movie-version of Ella Enchanted, the Big Bad Prince Edgar defeats himself with the poisoned crown he planned on using to kill his nephew and heir by putting it on during his Motive Rant at the end of the movie.
 * Indiana Jones twice, in 'Raiders of the Lost Ark the Nazis opened the Ark of the Covenant themselves and its powers then disintegrated them a very painful manner. Then in Indiana Jones and the Kingdom of the Crystal Skull'', Colonel Spalko wanted the skulls to tell her everything, and they give it to her until she bursts into flames.

Literature

 * In Stardust by Neil Gaiman, there are two major villains, who effectively and elegantly dispose of each other when the heroes aren't even around.
 * In the film version, three out of the five villains die at each other's hands.
 * Likewise, the climax for Robin Cook's Vector has the two villains polish each other off.
 * In earlier The Dresden Files books, human villains have a tendency to kill each other, be hoist by their own petard or killed by side characters... so Harry doesn't have blood on his hands and The White Council doesn't get angry at him.
 * Of course, the rules of magic only state that you cannot kill people with magic. Evidently, they don't care so much if you just pull out a gun and shoot them.
 * Murphy would, though.

Live Action TV

 * This was very common in the early seasons of Smallville with the krypto-freaks. If they didn't somehow lose their powers they inevitably met a messy end at their own hands.
 * Major trope of Buffy, particularly in the early seasons. Human villains tended to fall into pits of their own monsters while Buffy tried in vain to save them. See especially "The Pack" and "Go Fish".
 * In the Angel episode "Supersymmetry" Fred attempts to kill the villain who, years earlier, had trapped her in Pylea, a demon Hell Dimension, by sending him through one of his own portals. When her boyfriend, Charles Gunn, intercedes, he explains that if she kills him in revenge she will never be the same. Gunn then snaps his neck and throws him into the portal, and they tell the rest of the heroes that this trope happened and he fell into his own portal.

Web Original

 * Subverted and inverted in the ending of Super Meat Boy. Dr. Fetus seems to be killed by his own Dying Moment of Awesome, but then he pops up again, only to be crushed helpless by Bandage Girl.

Web Comics

 * In El Goonish Shive, Damien. Though it's sort of Justified for Villainous Breakdown of someone who was batshit insane to begin with.
 * Subverted in Order of the Stick, where Kubota cleverly surrenders right before Elan is going to kill him as revenge for . Kubota realizes that he can probably get acquitted in a trial, and that Elan is too heroic to kill him in cold blood. Double Subverted, however, because Vaarsuvius isn't that heroic.