Kytheon's Tactics is a common Sorcery card from Magic Origins (ORI), collector number 25. Current market price: $0.10 (foil $0.10), TCGplayer market prices via Scryfall.
Creatures you control get +2/+1 until end of turn. Spell mastery — If there are two or more instant and/or sorcery cards in your graveyard, those creatures also gain vigilance until end of turn. (Attacking doesn't cause them to tap.)