Obuun, Mul Daya Ancestor is a mythic Legendary Creature — Elf Spirit card from Zendikar Rising Commander (ZNC), collector number 8. Current market price: $1.64 (foil $1.27), TCGplayer market prices via Scryfall.
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.