The Damaged, God-Eater

Flying, Undying, Ward {3}
Contagion 3 (Whenever this creature deals damage
to another creature, that creature gains Rot 3 - at the beginning of your upkeep, put 3 -1/-1 counters on this creature.)
Whenever a creature an opponent controls with
1 or more -1/-1 counters on it would die, instead
remove all -1/-1 counters from that creature and
gain control of it.