Horned Stoneseeker is a uncommon Creature — Lizard card from The Brothers' War (BRO), collector number 138. Current market price: $0.11 (foil $0.23), TCGplayer market prices via Scryfall.
Menace When this creature 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.") When this creature leaves the battlefield, sacrifice a Powerstone.