Mitosis worked for Regalia and attacked Newcago under Regalia's orders. He is classified as a High Epic, although he is killable via conventional means.
Mitosis can split into two. Neither of the two Mitosises are considered originals, and both possess Multicellular Division. The two results possess all clothing, weapons etc of the original.
Multicellular division cannot be rescinded, the only way to remove a clone is to kill it. Each clone causes the intelligence of all clones to fall, but this issue was corrected by Calamity (character). Each new clone also destabilizes the molecular structure of all other clones, and all clones can communicate instantly and wirelessly. If there are too many clones, firing a handgun will cause the bullet to disintegrate mid flight and the gun to explode (Newton's Third Law).
If Mitosis hears music from his band, his molecular structure is further compromised based on volume. If there are too many clones, a large number will disintegrate due to the wireless communication. Mitosis is the only Epic who can be killed with only his weakness, all other High Epics require their weakness employed in conjunction with a conventional lethal weapon.