100 Reasons Why The Villain Doesn’t Kill The Heroes When They Have The Chance

When the Villain has the chance to finish off the heroes, why don’t they?

1There isn't enough time to kill the Heroes – they are only seconds away from being destroyed themselves unless they flee the area now.
2If the Heroes are allowed to survive and escape, they will end up revealing key intel to the Villain (for instance, they can follow them back to the rebel base).
3The Villain will kill the Heroes, but first they must be interrogated – they hold information vital to the completion of the Villain's Master Plan.
4The Villain is deeply superstitious or religious, and the signs/omens indicate that killing the Heroes now would bring great misfortune on them. The Villain desperately wishes that it would be okay to kill them now, but they fear the wrath of the Gods, so they will imprison them until the Omens change, which will surely be by the next Moon.
5The Villain is currently being observed by someone whose approval they deeply need, and who wouldn't like seeing the Heroes be killed in this way, at this moment. Perhaps the Villain is a protective parent trying to shield their child from the violence that their chosen path necessitates, or maybe they are a political figure that cannot publicly execute the heroes like this without losing popular support.
6The villain finds the PCs amusing and wants to watch them struggle.
7The villain isn't actually evil. They are a good person that somehow got possessed by an evil entity. As the villain is about to finish off the heroes, the disgustingly evil act they are about to do causes the villain to gain enough control to fight with this entity. Ultimately this entity regains complete control, but not before the heroes had enough time to escape.
8A former enemy of the party that never defeated them shows up and drives off the villain, this person tries everything to become able to defeat the party and won't let the villain take that from them.
9The villain has limited resources and is in danger of needing them for a threat bigger than the heroes (think two rival archmages).
10The villain isn't the BBG, just a lieutenant, and has a last minute (or long matured) change of heart.
11The villain just fought the heroes to test himself / test something / prove his point, and had no intention of killing them in the first place.
12The villain is in a rush for a bigger goal than getting rid of the heroes (like being the first of 3 parties to reach the end of the dungeon).
13The villain suddenly loses control of a source for his powers (hey, it isn't Deus ex machina if it's known beforehand, and more, if the heroes had managed to shorten his time in control of the source).
14The environment of the fight is damaging to the villain, and he decided the heroes are not worth the risk of getting more injured (like, if he needs to be constantly underwater, or close to his mother brain).
15The villain is frail / sick and has a frequent need of healing.
16The villain doesn't see the heroes as a threat, and intends to enslave them, or simply lock them up for life and stop thinking about it.
17The villain just wanted a snack, and one of the heroes' allies is just enough.
18The villain is terrified of damaging his lair even more.
19One of the heroes has robbed his treasure, and killing them would destroy it or make it harder to find / get back.
20The villain wishes to crush the hopes of the people. If they crush the party like ants now, they will serve as martyrs. But if he kills them when the time is right, it will kill their spirits.
21The villain intends to steer the heroes toward a confrontation with the fearsome rival. Whoever wins will be weakened and easy prey when she arrives to finish them off.
22These heroes have the potential for tremendous growth in power and fame. Let them grow. I will be known as the conqueror- not of kobolds, but of dragons!'
23The villain has destroyed countless enemies, and now foresees a time when no one worthy remains to cross swords with, to threaten, to gloat to. He is loath to admit it, even to himself, but fears being alone.
24The villain has allowed the heroes to acquire certain misinformation. They must be allowed to spread it.
25Destroy them? But I created them for a purpose, and they have yet to fulfill it.'
26Someone important knows the PCs whereabouts, and if they turn up dead, can send more troublesome henchmen.
27It is customary for persons of the PC's stature to be ransomed, and it is considered entirely barbaric to murder people you have imprisoned in your dungeon. The villain hasn't quite decided on how to make it look like an accident first...
28The villain sincerely believes the PCs can be bought or swayed to his side.
29The villain is part of a group which takes murder very seriously (for example, la cosa nostra). He needs to get the blessing of someone higher up first. He'll happily break some legs for the time being, however.
30The villain wants to turn this inconvenience into a boon- feed them to shapeshifters, make them unwilling suicide bombers, use them as guinea pigs, etc.
31The villain is in love with one of the party NPCs.
32The villain, while villainous, is actually terrified by the sight of blood.
33The villain just... Doesn't feel like it today. Even they're not entirely sure why, but the whole idea of killing someone today just doesn't strike their fancy enough to actually bother.
34By letting them go now, the heroes will be in more danger later. Ie: one of the party has a magical explosive planted on their clothing that will go off once they reach the hero base/ship.
35The villain psychically feeds on pain, misery and humiliation, and wants to prolong this meal (maybe like aging a fine wine) by imprisoning, rather than killing, the PCs.
36The villain thinks they have information about a rival faction, which must be extracted from them before killing them (and the villain can’t force corpses to talk).
37The villain wants to send them to infiltrate a rival faction (none of their own conventional forces can pass themselves off as members of that faction). Maybe it’s a suicide mission. Maybe PCs are fitted with ‘compliance’ neckbands which ‘detonate’ if they go off mission. Maybe the PCs will be Trojan Horses for scrying, infection, or a 'portal', as others have mentioned.
38The villain wants to feed/give them to someone or something else - alive…
39The villain wants to use them as fighting practice for his lieutenants. Especially if their race is extraplanar and they know little about this plane’s fighting styles and peoples.
40The villain foresees that a rival group of adventurers is approaching. They need to prepare to defeat that group - and wish to capture both groups so that they can pit the rival parties against each other as gladiators in an arena in a forthcoming event.
41The villain has seen something in one of the Heroes, something they can use.
42The villain isn’t concerned enough with the players to view them as a threat.
43The villain is fundamentally bored with life, mostly just going through the motions since they don’t really meet any meaningful challenges in their day-to-day life. They don’t kill the heroes because are/have the potential to become a meaningful challenge, and they crave that.
44The villain refuses to kill an honorable adversary.
45The villain refuses to kill anyone because they don’t think of themselves as the villain.
46The villain believes death is a reward the players haven’t earned.
47The villain swore to their lost love not to kill in pursuit of his goals.
48The villain views the players’ opposition as philosophically inevitable and therefore a good thing.
49The villain wants the players to stop her, either consciously or subconsciously.
50The villain respects the players and believes they will eventually see the error of their way and join her.
51The villain doesn’t really understand why the players are trying to stop him. It’s all fun and games to him.
52The villain believes the players are necessary to their legacy—they are the only ones he trusts to tell his story.
53The villain doesn’t understand death so killing someone doesn’t really seem meaningful to her.
54While the villain is absolutely evil, he's more a white collar criminal. He launders money, fixes bets, etc. He isn't a murderer.
55The villain is doing bad things to accomplish a greater good. They don't want to kill the heroes. They will only kill them if there doesn't seem to be any other way to accomplish their end goal.
56There isn't enough time to kill the heroes. Part of the villain's plan is time critical, forcing the villain to flee before they can eliminate the pest.
57There is a place the villain can't go. They need to trick the heroes into going there to (do something, obtain something).
58The villain gets summoned by their 'boss' before they can finish off the heroes.
59The villain already activated the machines or started the ritual that will transport them to where they need to go. The villain vanishes before they can finish off the heroes.
60The villain is the future version of one of the heroes. They can't kill that hero without creating a time paradox and ceasing to exist. They can't kill the other heroes without drastically altering their past in unpredictable ways.
61The villain is insane. They would miss their games, if they eliminate the other players (the heroes).
62The heroes include a family member of the villain. Father/mother or son/daughter. They could have known the whole time or revealed in the moment.
63In devouring the soul (or similar evil) of one of the fallen characters, that character's will is so strong or dark that it causes psychic trauma to the villain, who staggers off. That character's soul is gone forever but the rest of the characters survive or recover.
64The villain is prone to personality shifts and at the moment they feel merciful and will not kill the heroes.
65The villain uses a magic that makes them very powerful for a short time. That wears off and they are frail, old, or wounded and unable to finish off the party.
66Villain whispers into each character's ear while they lie prone: 'Act as if you are dead and act well. The [Secret Malevolent Entity] is watching' before giving a nonlethal 'killing' blow.
67The doomsday, summoning ritual, or other device that is supposed to consume their souls or magics malfunctions. The villain leaves with a promise that they'll consume them later.
68The players are to be used as part of a human sacrifice ritual later, so are preserved and bound.
69One of the lieutenants reminds the villain that the party doesn't even know who they really are. The villain laughs, says the fun isn't over, and leaves the party with the question of who the villain really is.
70The villain's lieutenant has a change of heart due to the suffering or cruelty or backstory reveal. The sudden betrayal catches the villain off-guard and they leave, potentially wounded.
71The magic that the villain uses to finish off their victims never actually kills them, perhaps unbeknownst to the villain. It instead banishes their soul to another plane or similar. For example, sends them to the Feywild, to plane of shadow, into the service of a devil, into the future, or into the murder weapon itself.
72They 100% want to kill the PCs... but something whispering guidance into their ears wants them alive for some reason.
73The villain is attempting to fulfill an ancient prophecy, and the death of the PCs now doesn't mesh with their interpretation.
74Fighting against the PCs is the most fun they've had in ages, and if they execute them the fun ends.
75The PCs were unwittingly infested with magical parasites earlier in their adventures, and the Big Bad wants them to complete their gestation cycle.
76The villain is convinced that he can convince one or more PCs to flip to their side. He leaves the rest alive as well, knowing that it will be much harder to make their sales pitch if their hands are covered in the blood of the real target's comrades.
77The villain follows a particular sect of evil worship that believes that dead enemies go off to their normal afterlives, but the broken and subservient follow you to the hells to serve as your slaves and army. They became tyrants in life so they could be a conqueror in death, and want the PCs, some of the strongest fighters in the land, in their damned legion.
78The villain is an emotion-sensitive cannibal; just eating someone is nice, but eating someone kept in a state of terror is so much better. And what could be more terrifying than the knowledge that an emotion-sensitive cannibal is just waiting for the right opportunity to string you up by your ankles and literally butcher you like a squealing pig?
79The villain mistakes or worries that the party is representative of another important faction that the villain doesn't want to anger. A misunderstood phrase or outfit leads them to believe the party is a part of that group.
80The villain's lieutenant is a plant from another faction and says something to spare their lives, either dealing nonlethal killing blows, telling the boss they're dead, or staying the villain's hand in some way.
81The villain chops off the hand of each downed opponent and leaves them to their misery. (Cue a side quest to heal their hands back and then back for revenge)
82The villain underestimates them and leaves them to bleed out with no hope in sight. When the villain is gone, one of the characters is pretending death or another savior arrives just in time.
83A huge explosion happens for some reason, covers the party with dust, debris, and smoke, and the villain makes his retreat.
84The villain drains their blood, uses magic to drain their essence or something similar. It should leave them as a dying husk but instead they are able to recover.
85The villain thinks they have seen a prophecy of the party's death and it's not here, not today. 'But there is no need to rejoice-- I have seen it. Those of you who survive long enough, I will take your lives with my own hand.'
86The villain has secretly taken a grave wound and only reveals that once the players are beaten. He staggers, bleeding or bent back home to save himself.
87An intelligent weapon used by the villain refuses to kill one of the party members for some bizarre reason (e.g. patron, looks, backstory secret, etc) The frustration and anger sends the villain away fuming.
88Trying to kill the villain aside, the heroes' actions are actually beneficial to the villain (for example, the artifact they both are looking for requires a sacrifice, and he wants to reclaim it from them afterwards).
89The battle has made the building unstable and the creeking, falling debris, or weak flooring prevents the villain from approaching to finish the deed.
90The villain is too focused on the prize they are after that is nearby and rushes to capture or gather that.
91Come now, really try this time, would you?' The villain madly enjoyed that battle and heals the party to give it another go.
92The villain burns the body of the most powerful member and leaves the rest of the party to suffer. 'You are nothing without them, enjoy your miserable lives.'
93The villain finds a very interesting item among the party's loot and gets distracted, leaving them there.
94One of the heroes reminds the villain of himself when he was younger/more idealistic.
95The stakes are too personal for the villain and he wants to ensure the heroes die in the most painful way possible.
96The villain is skilled in divination and knows that killing the heroes now will result in some event that would be unfortunate for him.
97The heroes helped one of the villain's lieutenants earlier, who asked the villain to spare them this one time.
98The villain is bound by honor, and can't bring himself to kill a helpless person.
99The villain has a split personality, and the personality that just emerged is more inclined to spare the heroes.
100The villain carries some bloodthirsty entity within himself, and feels that killing any more people will unleash it.