Herald of War is a rare Creature — Angel card from Avacyn Restored (AVR), collector number 24. Current market price: $3.23 (foil $10.43), TCGplayer market prices via Scryfall.
Flying Whenever this creature attacks, put a +1/+1 counter on it. Angel spells and Human spells you cast cost {1} less to cast for each +1/+1 counter on this creature.