Wavewalker

Whenever another creature enters the battlefield, tap it. It doesn't untap during its controller's next untap step unless its controller pays {1}.
Megamorph {4}{u}{u} (You may cast this card
face down as a 2/2 creature for {3}. Turn it face
up any time for its megamorph cost and put a +1/+1 counter on it.)