Gryffwing Cavalry is a uncommon Creature — Human Knight card from Innistrad: Double Feature (DBL), collector number 283. Current market price: $0.22 (foil $0.69), TCGplayer market prices via Scryfall.
Flying Training (Whenever this creature attacks with another creature with greater power, put a +1/+1 counter on this creature.) Whenever this creature attacks, you may pay {1}{W}. If you do, target attacking creature without flying gains flying until end of turn.