Moonstone Harbinger is a uncommon Creature — Bat Warrior card from Bloomburrow (BLB), collector number 101. Current market price: $0.26 (foil $0.34), TCGplayer market prices via Scryfall.
Flying, deathtouch Whenever you gain or lose life during your turn, Bats you control get +1/+0 and gain deathtouch until end of turn. This ability triggers only once each turn.