Necalli, Devourer

You may exert Necalli, Devourer as it attacks.
When you do, it deals deals 2 damage to target
creature without flying.
At the beginning of each end step, if a creature
that died this turn was dealt damage by Necalli,
Devourer, put a +1/+1 counter on Necalli,
Devourer. Then, if there are three or more +1/+1
counters on Necalli, Devourer, transform it.
"Devour-our-our..."