Maggot Brood

Whenever a non-token creature dies, put a +1/+1
counter on Maggot Brood

When Maggot Brood dies, create X 1/1 tapped
Maggot creature tokens with "When this creature
dies, put a -1/-1 counter on target creature" where
X is Maggot Brood's toughness.

"Killing it wasn't too hard, we clapped each other on
the back. Then its whole corpse began to writhe."