A Proposal

A Proposal can't be countered.
If A Proposal wasn't cast from your hand by paying its mana cost, you lose the game.
Search your library for an artifact card, a creature card, an enchantment card, an instant card, a planeswalker card and a sorcery card. Cast those cards without paying their mana costs. You can't cast any other spells this turn. Then shuffle your library. Exile A Proposal.