Vert, Survivor of Jund

Devour 1 (As this enters the battlefield, you may
sacrifice any number of creatures. This creature enters
the battlefield with that many +1/+1 counters on it.)
Whenever you sacrifice Vert, Survivor of Jund,
you may pay {x}{b}, where X equals its power. If
you do, return it to the battlefield at the
beginning of the next end step with X +1/+1
counters on it.