Stone Retrieval Unit is a common Artifact Creature — Construct card from The Brothers' War (BRO), collector number 248. Current market price: $0.13 (foil $0.21), TCGplayer market prices via Scryfall.
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.")