Koilos Roc is a common Creature — Bird card from The Brothers' War (BRO), collector number 55. Current market price: $0.05 (foil $0.07), TCGplayer market prices via Scryfall.
Flash Flying 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.")