Sonny the Cuckoo Bird

As Sonny the Cuckoo Bird enters the battlefield, choose a creature type.
Whenever a creature with the chosen type enters the battlefield, put two
+1/+1 counters on Sonny the Cuckoo Bird.
Whenever Sonny the Cuckoo Bird attacks, its gains flying and +X/+0 until end of turn, where X is equal to its power.