Congregation Gryff is a uncommon Creature — Hippogriff Mount card from Outlaws of Thunder Junction (OTJ), collector number 200. Current market price: $0.25 (foil $0.28), TCGplayer market prices via Scryfall.
Flying, lifelink Whenever this creature attacks while saddled, it gets +X/+X until end of turn, where X is the number of Mounts you control. Saddle 3 (Tap any number of other creatures you control with total power 3 or more: This Mount becomes saddled until end of turn. Saddle only as a sorcery.)