Zengu, King of the Skulls

When a nontoken creature enters the battlefield
under your control you may put a -1/-1 counter
on it. If you do create a 0/2 black Skull creature
token with indestructible.
{b}: Put a -1/-1 counter on a nontoken creature
that has no -1/-1 counters on it, create a 0/2
black Skull creature token with indestructible.
Zengu's power is equal to double the number of
Skull creature tokens you control.