Gila Courser is a uncommon Creature — Lizard Mount card from Outlaws of Thunder Junction (OTJ), collector number 124. Current market price: $0.21 (foil $0.26), TCGplayer market prices via Scryfall.
Whenever this creature attacks while saddled, exile the top card of your library. Until the end of your next turn, you may play that card. 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.)