Sirius Black, Exiled Protector

Unleash (You may have this creature enter the battlefield with a +1/+1 counter on it. It cant
block as long as it has a +1/+1 counter on it.)
Whenever a creature you control duels, roll
two D20s instead. Choose one of the results
and disregard the other. Whenever a D20
roll is failed, transform Sirius Black.