Tormenting Shadow

Haunt (When this creature dies, exile it haunting
target creature.)
At the beginning of your upkeep, put a -1/-1
counter on the creature Tormenting Shadow
haunts. Then you may pay {x}{b}, where X is the
number of -1/-1 counters on that creature. If you
do, return Tormenting Shadow from exile to the
battlefield under your control with X +1/+1
counters on it.