Gayu's Dream Door

When you draw your first card each turn, you may reveal it. If you do, and if it's a land card, you may draw a card.
{4}{u}{u}{u}, Sacrifice Gayu's Dream Door: Exile the top ten cards of your library. As long as those cards remain exiled, you may cast up to two noncreature cards exiled this way without paying their mana costs.