Starseer Mentor is a uncommon Creature — Bat Warlock card from Bloomburrow (BLB), collector number 233. Current market price: $0.23 (foil $0.33), TCGplayer market prices via Scryfall.
Flying, vigilance At the beginning of your end step, if you gained or lost life this turn, target opponent loses 3 life unless they sacrifice a nonland permanent of their choice or discard a card.