Destructive Dragon

Trample, Flying, Devour X (As this creature
enters the battlefield, you may sacrifice any number
of creatures. This creature enters the battlefield with
X +1/+1 counters on it for each creature sacrificed
this way.)
Hellbent —If you have no cards in hand, Destructive Dragon has "{x}{b}{r}: Monstrosity X"
(If this permanent isn't monstrous, put X +1/+1
counters on it and it becomes monstrous.)