Jack Bauer, CTU Agent

When Jack enters, create a legendary artifact token
Nuclear Bomb with "This enters with 5 charge counters. Whenever it has either 0 or 10 charge counters, sacrifice it. When it leaves the battlefield, all creatures get -X/-X where
X is the number of charge counters on it. On your
upkeep, add 1 charge counter to it."

{t}: Sacrifice target creature. Remove up to X counters from target artifact where X is the sacrificed creature's power.

{u/b}: Regenerate.