Ovar, Woodcutter Vandal.

Haste, menace (Ovar, Woodcutter Vandal can't be blocked except by two or more creatures)
Whenever Ovar deals combat damage to a player,
put a +1/+1 counter on him.
As long as Ovar has a +1/+1 counter on him, it's
a werewolf in addition to it's other types and has:
"At the beginning of each end step, if no spells
were cast last turn, transform Ovar."