Dementia Sliver is a uncommon Creature — Sliver card from Time Spiral (TSP), collector number 236. Current market price: $0.36 (foil $4.00), TCGplayer market prices via Scryfall.
All Slivers have "{T}: Choose a card name. Target opponent reveals a card at random from their hand. If that card has the chosen name, that player discards it. Activate only during your turn."