Obuun, Mul Daya Ancestor
Legendary Creature - Elf Spirit | Power/Toughness: 3 / 3 (CMC 4)
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 enters the battlefield under your control, put a +1/+1 counter on target creature.