Stalking Snarler

Whenever Stalking Snarler enters the
battlefield, you may put a -1/-1 counter on
target creature you control. If you do, put a
+1/+1 counter on Stalking Snarler.
{1}{b}, Sacrifice Stalking Snarler: Draw cards
equal to how many -1/-1 counters are on all
creatures you control.