— Iron Man, dropping a terrorist before his victims
The hero has the villain at his mercy. He can kill him right here — but he won't. It's not because he would be stooping to the villain's level, or because letting them live would be more of a punishment. No, rather than killing the villain himself, the hero will instead leave him to the tender mercies of his victims, usually with some variation on the trope name. He may arm the victims first.
Slaves, oppressed citizens, abused prisoners, terrorized villagers, tortured laboratory subjects and the families of the victims are the most commonly used.
Differs from The Dog Bites Back in that that is a form of Karmic Death, while with this one, the hero deliberately sets it up. A subtrope of Throw Em To The Wolves.
As a way for a villain to meet their demise, this can easily be a Death Trope. Expect unmarked spoilers.
In DC The New Frontier, Wonder Woman, after defeating some enemy soldiers, gives their weapons to the women they'd been using as sex slaves. One guess as to what they do with them.
Ironman: (After defeating a bunch of mooks except for their leader, which he hands over to the victims) "He's all yours."
In their second miniseries, the Secret Six do something similar with the inmates of a North Korean prison. They also do it later in their ongoing when they hand a childkiller over to the father of one of his victims (although he did hire them to do it), Catman even giving him instructions on how to most effectively torture him to death.
Jonah Hex: Jonah hands an Indian-butchering sheriff over to the tribe he's been preying on, but then subverts it in another issue, where he hands a murderess over to the carnival who hired him, but when he sees them start to enact "carnival justice" which involves beating her to death all night long, he puts a bullet in her head.
Inverted in Spawn, where Spawn uses his powers to turn a Ku Klux Klan leader black and then leaves him to be found by his fellow Klan members, who lynch him.
Magicka: The heroine at one point encounters Hitler (the most evil men Earth produced were assembled in one point in time and space) but is prevented from killing him. Later on, she teleports him, in full uniform, into the middle of a crowd of prisoners in Auschwitz, circa 1942. The view then pans out to the silent crowd holding boards with nails in them...
In an issue of Green Lantern: Emerald Warriors, Guy Gardner disarms some sadistic alien slave drivers and leaves them to the picks and shovels of their charges. However, this is taken as a bad sign that the trace of Red Light inside him may be growing.
A non-lethal variant in an issue of Preacher has Jesse drive the local KKK leader (in full uniform) into the black part of town and dump him out in front of a bar.
In one of the grimmer Batman story arcs, The Cult, the Dark Knight is captured by a cult and brainwashed into helping them kill their way through Gotham. He manages to break free and later returns to bring down the leader, Deacon Blackfire. Knowing that giving Blackfire a well-deserved death would only serve to make him a martyr, Batman focuses on causing as much pain with every blow as possible. Eventually Blackfire breaks and begs for mercy, in front of the throngs of cultists. The fatal element of this is that part of Blackfire's creed that he hammered into the heads of his kidnapped followers was that their substantial suffering was insignificant in the greater scheme of things. To show himself to be weak and submissive enraged the people that had suffered greatly for him, and the disillusioned cultists tore him apart so ferociously that nothing identifiable remained.
Nextwave: The squad does this by accident. Upon de-transforming a police officer who had been changed into a giant mecha, they leave him in the care of a crowd that claims to be his friends. In his weakened state, they don't notice his panicked eyes and whispered protests, and don't know that the cop is extremely corrupt and they just handed him over to the people he's been terrorizing and extorting for the last twenty years.
X Man: In issue 66, Nate Grey learns that the monster from whom he'd been defending a group of mutant Corrupt Corporate Executives was targeting them because they stole his race's children in order to harvest and sell their organs, Nate executes most of the group himself, but he singles out the one who had come up with the idea to steal the children, and delivers her alive to the monster and his people.
The Authority does this to one unnamed Indonesian general when he claims they wouldn't kill him as this would bring the rest of the world's governments on them. they reply that they won't do anything to him but drop him off (in the middle of a slum that had particularly suffered from his actions).
In Incorruptible, Max Damage drops a gang of murderous white supremecists off in the middle of an ethnic neighborhood they terrorized.
In the Pony POV Series7 Dreams/Nightmares Gaiden series, Patch, having become anAction Girl due to her journey to reconstruct the Rainbow of Light after the G2 world suffered an apocalypse, gets brainwashed by Film Critique, the Pegasus Despot using the Shard of Laughter to become anEvil Overlord, and turned into a member of his brainwashed harem. After spending an undisclosed number of days as his Sex Slave with the rest of the harem, she's freed by Brightglow. She then steals the Shard back, purifying it (due to fitting the profile of a proper Bearer of the Element of Laughter), breaking his spell. She proceeds to shoot him in the leg, arm his now unbrainwashed harem with swords, and leave him to his Karmic Death at their hooves. She also stole all the ammo of his willing guards. She apparently did this to several other people who were abusing the Shards and even admits she has a habit of doing so.
In The Hunting Party, the protagonists ultimately succeed in capturing a Serbian war criminal. They drive to a town he persecuted, leave him in the town square, and drive away. We don't see his fate, but it was probably unpleasant.
In the first Iron Man 1 movie, after Tony's first 'live-fire exercise' with the completed armor, he leaves the leader of the 10 Rings Mercenaries to the mercy of the villagers they'd been terrorizing, after disarming him.
Seven Samurai has an unusual variant of this trope. The samurai capture a bandit and immediately have to protect him from the (justifiably) murderous villagers. However, when they are approached by the oldest woman of the town, who lost every member of her family to bandits and has since been almost unwilling to continue living, they quietly step aside and allow her her vengeance.
In Rise of the Planet of the Apes, ape hero Caesar refuses to save Jacobs and leaves him hanging on the side of a bridge to the scarred, Devil in Plain Sight bonobo Koba, who is bitter after having been the subject of human experiments for years. Koba is visibly delighted when he throws him to his death.
In The Painted Bird, there are some Nazi-aligned Polish partisans who have been raping women and basically torturing and killing everyone in the village they enter. They are defeated by Communist partisans who hand them over to the townspeople, who brutally torture them to death.
Attempted in Sandman Slim - it doesn't quite take, as Mason survives the pounding by the Hellions and ends up gaining (at least political) power again.
In Wolf Island by Darren Shan, Grubbs, having promised Antoine that he won't kill him, proceeds to leave him to the tender mercies of a group of the werewolves he has been abusing in the name of science.
Grubbs Grady: I said I wouldn't kill you... but I said nothing about them.
Though Antoine is quite literally thrown to wolves, this does not fit the Throw Em To The Wolves trope, as Grubbs has no qualms about getting blood on his hands and is merely delegating the murder to circumvent his promise.
Finn decided that shooting was too good for them, so he went judge and used his squad as jury. They were stripped, hamstrung at ankles and wrists, turned over to women in Complex. Makes me sick to think about what happened next but don't suppose they lived through as long an ordeal as Marie Lyons endured.
In Shamran by Bjarne Reuter, the hero, Filip, confronts the officer in charge of "marking" the people of Tronn, a mandatory practice where any citizen (except for members of the government and the military) of a certain age has one of his/hers abilities (sight, hearing or speech) surgically removed. After disarming the officer, Flip throws him at the feet of the patrons in one of the capitols larger inns, all of them people the officer so zealously have marked throughout his life. In the next scene, the guards of the capitol's castle gets a nasty surprise in form of the officer, now blind, deaf, and mute, fumbling and crawling around in the dirt in front of them.
Ged does this in the third book of the Earthsea Trilogy. On a slaver ship. Where there are only half a dozen slavers. All he needs is to remove the slaves' chains.
Daniel Waterhouse: You speak of putting Jeffreys to death with the strength of your right arm. Yet I tell you that if we must rely on your arm, strong as it is, we would fail. But if, as I believe, England is with us, why, then we need do no more than find him and say in a clear voice, 'This fellow here is my lord Jeffreys,' and his death will follow as if by natural law, like a ball rolling down a ramp.
Daniel Waterhouse (some time later): I apologize for the disruption. You have heard of Jeffreys, the Hanging Judge, the one who decorated trees in Dorset with bodies of ordinary Englishmen, who sold English schoolgirls into chattel slavery? [...] The man I speak of, whose name you have all heard, the man who is responsible for the Bloody Assizes and many other crimes besides-judicial murders, for which he has never dreamed he would be made to pay, until this moment-George Jeffreys, Baron of Wem, is he. *points*
In the Star Wars Expanded Universe, the sadistic, pain-obsessed droid EV-9D9 has her limbs blasted off and is left to the mercies of the mutilated droids in her Torture Cellar. For extra points, her pain receptor and "pain vision" third eye are removed beforehand, robbing her of the sensation of her own destruction (which she had been anticipating).
In Kaiju War Chronicles, Match 113 ends with Glidor, the Mad Scientist who set up a Let's You and Him Fight between Frankenstein and King Kong, accidentally revealing to Frankenstein that he set the whole thing up. This enrages Frankenstein, but Glidor then reminds Frankenstein that the monster would never kill a human and thus won't kill him. Seeing this, Frankenstien frees Kong from his bonds and tells him that Glidor was the one who took him from his home island. Kong, now knowing who to blame for his kidnapping, sends Glidor on a one way flight into a mountain.
In the Agent Pendergast novel Brimstone, Reverend Buck leaves Hayward at the "mercy" of his followers after condemning her in front of them. He's well aware that they are itching to stone her to death.
In Kitty Norville, Kitty used to be part of a werewolf pack in Denver until she was exiled by their abusive leader, Carl. Later she gets drawn back into a local conflict and discovers that Carl has only gotten worse while she was away, ruling the pack with an iron fist. When she finally has Carl cornered, with a silver-loaded gun pointed at him and the rest of the pack closing in, Carl begs her to spare him. Kitty lowers the gun and says, "I'm sorry, Carl. That's not for me to decide." Then the whole pack descends on him and rips him to shreds.
Live Action TV
In Babylon 5, Lord Antono Refa, a racist Centauri noble, responsible for the bombing of the Narn homeworld with Weapons of Mass Destruction and the mastermind of death camps and genetic cleansing programs, is handed over to a mob of Narn insurgents led by G'Kar. Instead of doing the deed himself, G'Kar calmly instructs his followers to make sure that the planted evidence is found and that Refa's head remains intact for identification.
In The X-Files episode "Sleepless", the Preacher lets the ghosts/apparitions of the Vietnamese civilians whom he and his unit killed during the War and who follow him around kill his former squad-mates and superiors.
Angel: A paranormal crime boss/casino owner comes to collect one of Angel's True Companions' souls. In the climax, Angel chops off the head of said crime boss. It quickly becomes apparent that this will only temporarily incapacitate him, so Angel asks who else in the casino owes the man, and leaves as the mob descends on the crime boss.
G.B.H.: In this British political comedy/thriller, the young thugs who have been stirring racial tensions by beating up black people while dressed as policemen are betrayed by their controller who hands them over to a gang of black rioters. They are only beaten up and humiliated rather than killed, but he doesn't seem to care; he laughs hysterically as he watches them dragged from their van.
Teyla uses the threat of this in order to get information on where the Athosians have been taken. She tells the man she will announce that he is a Wraith worshipper and leave him to the townsfolk. He gets VERY cooperative after that.
On the May 16th, 2011 episode of WWE Raw, Michael Cole is signing a contract for his match at Over The Limt with Jerry Lawler. In the middle of Cole's Breaking Speech, Jerry replies with a Shut Up, Hannibal!...then praises Cole's Dragon-in-Chief Jack Swagger. Cole replies that being Cole's "sideick" is the best thing that's ever happened to Swagger and no one remembers what Swagger was ever the champion. Cue Swagger getting absolutely furious with Cole. However, instead of beating down Cole himself, he simply looks over Cole's shoulder to Jerry and says "He's all yours" and walks out of the ring, leaving Cole completely alone going into his match at Over The Limit with a justifably furious Lawler who beats the stuffing out of Cole and subjects him to a priceless Humiliation Conga. Though this may have been invoked by Lawler via Batman Gambit.
There are multiple cases of wrestlers, standing in the ring with someone The Undertaker is coming to beat down, shoving that person directly into Taker's arms and leaving the ring post-haste.
Myst V: In the climax, villain Escher is captured by the freed Bahro, a slave race he had tortured and experimented on previously. Yeesha's instructions to them are to "treat him as one of the Least", making something of a Broken Aesop out of the whole episode.
There are few of these in Red Dead Redemption. Mainly (if not exclusively) when John is in Mexico helping out the revolution. In particular, there's the fate of Vincente de Santa: John can either finish him off personally or just walk off and let the rebels shoot him up.
Mass Effect 2: One of the possible endings of Jacob's loyalty mission is to just leave after having destroyed all the mechs that were protecting Ronald Taylor from the wrath of his feral former crewmates.
"You were a better man dead. Far as I'm concerned, you still are."
Knights of the Old Republic 2 can have you doling this one out on Atris. After it's clear her Knight Templar tendencies and collection of Sith holocrons have corrupted her, you can cheerfully lock her in her archive room with those holocrons and walk away.
Exile:Those are Sith Holocrons, Atris. They don't tolerate failure...
In Max Payne 3, as Max is holding Arthur Fischer, a corrupt surgeon who works for an organ thieving ring, at gunpoint, the standoff is suddenly interrupted by a visibly disturbed Serrano, the leader of slum-gang who had served as an antagonist for much of the plot, before he ended up being imprisoned along with the ring's other unfortunate victims. After a moment's consideration, Max lowers his gun, and allows his former enemy to kill the doctor with a scalpel.
At the end of Dirty Laundry, Frank Castle aka The Punisher leaves the violent pimp battered and soaked in the booze from his own bottle, then leaves a lighter on the ground for the hooker that the pimp had just abused. She chooses to light him up.
Superman The Animated Series: Superman tries this on Darkseid. It doesn't work out the way he intended — the slaves on Apokolips are too broken to even consider rebelling, and approach him with reverence and questions of concern for his well being; then they gently carry the injured Darkseid away to receive care.
"I am many things, Kal-El. But here, I am God."
Simba does this accidentally to Scar in The Lion King. Simba spared Scar from death, even though he doesn't think Scar deserves it, and tells him to go into exile, but Scar attacks anyway. Simba defends himself from Scar pouncing on him by kicking him over a ledge, where he meets the starving hyenas. Seeing as how Scar had, only moments ago, said that the hyenas were the true enemy, you can imagine what they proceeded to do with him.
Scar: Ah, my friends! Shenzi: Friends? I thought he said we were the enemy! Bonzai: Yeah! That's what I heard.
The Powerpuff Girls: In "Moral Decay," Buttercup has amassed a tidy fortune from the tooth fairy for teeth she has accumulated from punching the teeth out of all the robbers. When she attacks the show's main villains unprovoked, Blossom gets wind of it and she and Bubbles help the villains set up an ambush on Buttercup to teach her a lesson.
Buttercup: Uh, guys? A little help here?
Blossom: Sorry, Buttercup. You know what they say. "An eye for an eye..."
Ben 10 Ultimate Alien has Charmcaster leaving Darkstar weakened to be beat up by the heroes after discovering he had formed an Unholy Matrimony with her just to take advantage of her power and had no real feelings for her.