Slithermuse is a rare Creature — Elemental card from Morningtide (MOR), collector number 50. Current market price: $0.66 (foil $10.97), TCGplayer market prices via Scryfall.
When this creature leaves the battlefield, choose an opponent. If that player has more cards in hand than you, draw cards equal to the difference. Evoke {3}{U} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)