Nix, Tempobreaker

Nix, Tempobreaker can't be blocked.

Whenever Nix deals combat damage to a player,
that player exiles cards from the top of their library
until they exile an instant or sorcery card. You may
cast that card without paying its mana cost. Then
that player puts the exiled cards that weren't cast
this way on the bottom of their library in a random
order.