Martial Impetus is a uncommon Enchantment — Aura card from Bloomburrow Commander (BLC), collector number 108. Current market price: $0.27, TCGplayer market prices via Scryfall.
Enchant creature Enchanted creature gets +1/+1 and is goaded. (It attacks each combat if able and attacks a player other than you if able.) Whenever enchanted creature attacks, each other creature that's attacking one of your opponents gets +1/+1 until end of turn.