The First Sliver is a mythic Legendary Creature — Sliver card from Secret Lair Drop (SLD), collector number 1371. Current market price: $64.26 (foil $68.78), TCGplayer market prices via Scryfall.
Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.) Sliver spells you cast have cascade.