Va'lara, the Userpent

First Strike, Wither
Whenever one or more -1/-1 counters are put
onto a creature or when a creature with a -1/-1
counter on it dies, create a 2/2 black snake
creature token.
{2}{r/g}{r/g}: put a -1/-1 counter on target creature
with a -1/-1 counter on it.