Farrel's Mantle is a uncommon Enchantment — Aura card from Fallen Empires (FEM), collector number 2. Current market price: $0.20, TCGplayer market prices via Scryfall.
Enchant creature Whenever enchanted creature attacks and isn't blocked, its controller may have it deal damage equal to its power plus 2 to another target creature. If that player does, the attacking creature assigns no combat damage this turn.