Furnace Reins is a uncommon Sorcery card from March of the Machine (MOM), collector number 141. Current market price: $0.30 (foil $0.67), TCGplayer market prices via Scryfall.
Gain control of target creature until end of turn. Untap that creature. Until end of turn, it gains haste and "Whenever this creature deals combat damage to a player or battle, create a Treasure token." (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")