Obuun, Mul Daya Ancestor

Legendary Creature — Elf Spirit

At the beginning of combat on your turn, up to one target land you control becomes an X/X Elemental creature with trample and haste until end of turn, where X is Obuun's power. It's still a land. Landfall — Whenever a land you control enters, put a +1/+1 counter on target creature.