Regeneration

Regeneration is the ability to regrow certain body parts or cells that have been dismembered or destroyed and replace them with brand new cells, or simply regrouping all of their separated parts back together.

Overview
There have been several beings capable of this, although each Mysterious Being has had different types of regeneration and different ways they have regenerated, and differed in how much time it takes to regenerate their bodies and whether they recreate cells in their body or regroup cells back together.

Some humans and Mysterious Beings have a weaker version of this ability, and are able to regenerate fractured bones or mutilated body parts.

Characters like Boros have an incredible rate of regeneration, with Boros himself surpassing all others of his race as stated by himself. He has been shown to regrow an arm in seconds just by concentrating his energy on it. When struck by Saitama's Consecutive Normal Punches, he was blown apart but was able to regenerate his whole body in an instant. However, Boros' regeneration ability has a limit, as it is shown in the end of the fight with Saitama, where he was unable to regenerate again after being struck by Saitama's Serious Punch due to him already having used up all his energy.

Black Sperm possesses a unique regenerative ability; as his body is formed from vast numbers of copies of himself working together, any damage he sustains will reduce his total count, but his body is able to fully regenerate so long as he has reserves. Even if he is cut to pieces, his severed body parts will reform into more copies of himself.

Orochi can regenerate his body from the brink of death by absorbing the blood of other creatures. However, it is only shown that he can regenerate from his heart.