Sunbird's Invocation [Ixalan]

Set: Ixalan Type: Enchantment Rare Cost: {5}{R} Whenever you cast a spell from your hand, reveal the top X cards of your library, where X is that spell's converted mana cost. 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.