Sarinth Greatwurm is a mythic Creature — Wurm card from The Brothers' War Promos (PBRO), collector number 220p. Current market price: $1.11 (foil $0.97), TCGplayer market prices via Scryfall.
Trample Whenever a land enters, create a tapped Powerstone token. (It's an artifact with "{T}: Add {C}. This mana can't be spent to cast a nonartifact spell.")