Maw of Nightmares

Devour 1 (As this enters the battlefield, you may sacrifice any number of creatures. This creature enters
the battlefield with that many +1/+1 counters on it.)
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its
owner's control with a -1/-1 counter on it.)
{b}, Remove a counter from maw of nightmares:
Create a 2/2 black Nightmare Ooze token.