Mind's Dilation is a mythic Enchantment card from Secret Lair Drop (SLD), collector number 1180. Current market price: $13.64 (foil $14.96), TCGplayer market prices via Scryfall.
Whenever an opponent casts their first spell each turn, that player exiles the top card of their library. If it's a nonland card, you may cast it without paying its mana cost.