Gluttonous Monstrosaur

Whenever another creature enters the battlefield, Gluttonous Monstrosaur fights that creature.
(Each deals damage equal to its power to the other.)
Whenever Gluttonous Monstrosaur fights a
creature, at the beginning of the next end step,
put a +1/+1 counter on Gluttonous Monstrosaur.
Then if it has three or more +1/+1 counters on it,
you may transform it.