Merdragon

Devourmorph — X (You may cast this card
face down as a 2/2 creature for {3}. Turn it face
up any time by sacrificing X creatures and put
X +1/+1 counters on it.)
As long as Merdragon has a +1/+1 counter
on it, it has flying and trample, and it's a
Dragon in addition to its other types.