Mind's Dilation is a mythic Enchantment card from Eldritch Moon Promos (PEMN), collector number 70s. Current market price: — (foil $17.27), 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.