Trueheart Twins is a uncommon Creature — Jackal Warrior card from Amonkhet (AKH), collector number 153. Current market price: $0.05 (foil $0.18), TCGplayer market prices via Scryfall.
You may exert this creature as it attacks. (It won't untap during your next untap step.) Whenever you exert a creature, creatures you control get +1/+0 until end of turn.