Corpseborn Shrieker

Corpseborn Shrieker enters the battlefield with X -1/-1 and X Corpse counters on it.
Whenever Corpseborn Shrieker deals combat to a player, remove a -1/-1 counter from it and double the number of corpse counters on it.
Corpseborn Shrieker's power and toughness are each equal to 1 plus the number of corpse counters on it.