Quix, the Extractor

As Quix enters the battlefield, for each opponent search that player's library for a card with converted mana cost equal to or less than the amount of mana spent to cast Quix and exile them. Those players shuffle their libraries.
When Quix leaves the battlefield, choose a nonland card exiled with Quix and flip a coin. If you win the flip you may cast that card without paying its mana cost, otherwise its owner may.