Brightfield Mustang is a common Creature — Horse Mount card from Aetherdrift (DFT), collector number 5. Current market price: $0.19 (foil $0.28), TCGplayer market prices via Scryfall.
Whenever this creature attacks while saddled, untap it and put a +1/+1 counter on it. Saddle 1 (Tap any number of other creatures you control with total power 1 or more: This Mount becomes saddled until end of turn. Saddle only as a sorcery.)