Zarus, Maelstrom Breaker

Flying, haste
When you cast this spell, reveal the top X cards
of your library, where X is the amount of mana
spent to cast Zarthus. You may cast a card
revealed this way with converted mana cost X or
less without paying its mana cost. Put the rest on
the bottom of your library in a random order.
When Zarthus enters the battlefield, until the
beginning of your next turn, players can't cast
spells with converted mana cost X or less.