Regeneration, often referred to as a healing factor, is the ability to heal from wounds at an accelerated rate, with many characters proving capable of regenerating from wounds that would be lethal to normal humans.
It has several different levels that range in potency from what is essentially just faster natural healing to being able to regrow limbs or organs, or even a severed head.
Higher levels allow characters to regenerate from even more severe wounds, such as being blown to pieces, reduced to a single cell, vaporization, and even complete physical destruction and beyond.
Instances of characters being wounded and inexplicably recovering off screen should not be taken as evidence of regeneration unless supported by further context. This is due to reasons ranging from possibility of off-screen treatment to continuity errors. See this thread for reference.
Low: Merely an accelerated healing ability for normal wounds, allowing the character to heal wounds that would normally take days, weeks, or even months much more quickly, sometimes even in just seconds. For machines and vehicles, this would just be regenerating basic exterior damage.
Mid-Low: The ability to heal wounds that would normally leave large scars, such as severe burns or deep injuries. For machines and vehicles, this would be regenerating damage that would normally leave large dents and openings.
High-Low: The ability to regenerate severed fingers, toes, or ears, minor organ damage, and even potentially reattach lost limbs. For machines and vehicles, this would be regenerating some interior damage, along with some minor critically damaged or destroyed parts.
Low-Mid: The ability to regenerate lost limbs, and even from severe organ damage or destruction, including traditionally fatal wounds and disembowelment or horizontal bisection. For machines and vehicles, this would be regenerating minor parts and more extensive internal damage.
- Examples: Piccolo and other Namekians (Dragon Ball), Shirou Emiya / Saber with Avalon (Fate/stay night), Wolverine (Marvel Comics)
Mid: The ability to regenerate from decapitation or severe brain damage. For machines and vehicles, this would be regenerating from the destruction of critical parts, such as the engine.
- Examples: Dante (Devil May Cry), Lernaean Hydra (Mythology), Sayaka Miki (Puella Magi Madoka Magica)
High-Mid: The ability to regenerate from being blown / cut to pieces, or from a small piece of your body, such as your severed head, a single organ, or a finger.
- Examples: Meta-Cooler (Dragon Ball), Dio Brando (JoJo's Bizarre Adventure), Ryūko Matoi (Kill la Kill)
Low-High: The ability to regenerate from a very small piece of your body, such as a puddle or drop of blood, or even something as small as a single cell.
Mid-High: The ability to regenerate from being reduced to ash, dust, smoke, or vapor.
- Examples: Majin Buu (Dragon Ball), Dark Matter (Kirby), Deadpool and Hulk (Marvel Comics), Ban (Nanatsu no Taizai), Logia Devil Fruit users such as Portgas D. Ace (One Piece)
High: The ability to regenerate from scattered or lone molecules, atoms, particles, or even pure energy.
Low-Godly: The ability to regenerate from the complete physical destruction of your body, instead restoring it from your disembodied consciousness, whether that be your soul, mind, some other nonphysical aspect of yourself, esoteric or metaphysical energy, or something else.
- Examples: Dark Schneider (Bastard!!), Sosuke Aizen (Bleach), Doctor Manhattan (Watchmen) UlforceVeedramon (Digimon), Spawn (Image Comics), Hourai Immortals (Touhou Project)
Mid-Godly: The ability to regenerate even after being completely erased from existence, including mind, body, and soul.
- Examples: Lavos (Chrono), Millenniummon and its other forms (Digimon), Sailor Moon (Sailor Moon), Chara (Undertale), The Chaos Gods (Warhammer 40,000)
High-Godly: The ability to regenerate even after the totality of your existence is erased, alongside the reality that you are present within that exists up to your own dimensional level.
True-Godly: The ability to regenerate from being erased on a level beyond the confines and concept of dimensions.