Sai Sei "Regeneration"
Though healing themselves over time is normal for most warriors in Dragonball Z there are few who have the ability to regenerate limbs almost instantly. Piccolo is one of these people and often uses this when his arm or other limbs are severed from his body, a new limb appears in it's place and almost instantly the user is restored back to full health thanks to the Sai Sei technique.
Piccolo, Cell, and Buu can all regenerate.
Repairing your body from damage would heal you but take energy to do it.
Buu's regeneration takes energy to heal his body.
Buu is ***.
Therefore, Piccolo and Cell should have regeneration.