Willow heals herself with a wave of her hand
Regeneration was the ability to be quickly cured of a wound or to be reconstituted after amputation or destruction of a body part.
Examples
Slayer
Slayers could recover from even very severe injuries in remarkably short periods of time. Usually, Buffy was completely healed within 24 hours of being injured, though more serious injuries took at least a few days; Buffy suffered from a severe stab wound to the belly that required at least a few days to heal, and, according to Vi, was heavily bruised for several days after her second encounter with the Turok-Han. Also, Slayers could receive scars; Buffy had a scar left from The Master's bite on her neck, with Angel and Dracula biting her in the exact same spot.
Vampire
Vampires healed rapidly, albeit in a similar way to human bodies (Spike's broken back healed, but after months passed). When Angelus was beaten several times with a crowbar, he recovered in little over a minute and was able to engage in a full-blown sword fight with Buffy without any physical handicap. They could also have unhealable scars under certain conditions. Xin Rong used an enchanted sword to give Spike the scar on his eyebrow. Faith gave Kakistos a permanent scar and blinded him in the right eye. Ancient vampires could regenerate amputated body parts, but modern ones lacked this ability (like Claw) though they could be surgically reattached (like Spike). The surgical extraction of the heart like James or a powerful object as the Gem of Amara gave them the capacity to regenerate in a few seconds (like Harmony Kendall and Marcus).
Demon
- Even beheaded, the Brotherhood of Seven like Marc and the Deathwok Clan like Lorne had the capacity to resolder their head; with that, amputated on another being like the Nahdrah Demon; or to grow a new head like Jenoff, the Strom Demons and the Voynok Demons.
- Norman Pfister was, in fact, a sentient hive of maggots, capable of being transformed into a human and giving him the capacity to regenerate at will.
- If gathered, the body part of The Judge allowed him to regenerate.
- The Mok'tagar Demon had uncanny regenerative abilities. For example, Kathy Newman's loose toenails kept growing after being cut.
- The blood of a Mohra Demon, known as the "Blood of Eternity", was colored green, glowed and had uncanny regenerative properties, making them virtually immortal. This blood could also heal other beings, and was capable of transforming Angel back into a human being when his blood mixed with the Mohra's. If severely injured, Mohras would regenerate and grow both in size and strength. Following the destruction of the Seed of Wonder and hence the loss of magic, Mohra blood, instead of simply healing injuries, triggered perpetual painful regeneration in those who used it, with their bodies resembling massive tumours; Angel and Faith were forced to decapitate a group of people who had tried to use the blood to heal themselves.
- The mineralogy was also an effective factor for demons like Mohra Demon who required vast quantities of salt to live and Ethros Demon who sought out primordial volcanic basalt to regenerate when wounded or weakened.
- Tor was able to survive mutilation and reassemble himself.
- Strom demons possessed regenerative abilities so powerful they could grow their faces back after having it blown off with a shotgun.
- The Vengeance demon seemed to heal rapidly in few seconds. For example, Halfrek and Anyanka recovered very quickly from their wounds while they were pierced by a sword.
- Half-demons can also heal quickly from injuries. Beck can heal from a stake in the chest within a few hours. The Groosalugg heals on a similar level like Angel, a vampire over 200 years old.
Witches
- Willow regenerated herself from a massive ax blow to her back from Warren.
- Willow was able to heal the cuts and bruises on her face after a tense fight with Giles by waving her hand over her face, making the marks disappear.
- Willow had the power to regenerate the skin of her stomach after it was eaten by Gnarl. She did this by meditating, drawing power from the Earth.
- Willow easily healed herself after being lobotomized by a skinless Warren, despite the fact that she was near death. Willow then used her powers to heal some of injured soldiers and Slayers, but couldn't heal all of them because she didn't have enough "healing".
Other beings
- Ronald Meltzer could control his molecular structure at will, allowing him to remove his hands or eyes from his body to make them levitate.
- The demon Barney who auctioned organs stemming from demons and super-human beings had healing hands in his collection.
- Charles Gunn tried to contact Healers for to cure Winifred Burkle, dying because of Illyria. However, they refuse to cooperate, fearing the Old Ones.
- Severin could heal his wounds by absorbing magical energy. With sufficient charge, he was able to survive and recover from a stake to the chest.
- The Medical Center of Arashmaharr had regeneration cream which could regrow lost limbs.
Behind the scenes
- In the post-After the Fall comics, which are dubious canon, Angel developed the ability to regenerate lost limbs, which he demonstrated after James ripped his hands and feet off. Illyria claimed the vampires of her time possessed such an ability[1].