Mesmeric Sliver is a rare Creature — Sliver card from Secret Lair Drop (SLD), collector number 620. Current market price: — (foil $0.66), TCGplayer market prices via Scryfall.
All Slivers have "When this permanent enters, you may fateseal 1." (To fateseal 1, its controller looks at the top card of an opponent's library, then they may put that card on the bottom of that library.)