Arm the Cathars is a uncommon Sorcery card from Innistrad: Double Feature (DBL), collector number 270. Current market price: $0.05 (foil $0.29), TCGplayer market prices via Scryfall.
Until end of turn, target creature gets +3/+3, up to one other target creature gets +2/+2, and up to one other target creature gets +1/+1. Those creatures gain vigilance until end of turn.