Yennett, Cryptic Sovereign

Because all attackers are chosen at once, a spell cast this way can't affect which creatures you can attack with, but it can affect which creatures will be able to block.

If the revealed card doesn't have an odd mana value or if that card does but you choose not to cast it, you draw a card. Keep in mind that revealing a card doesn't cause it to change zones. This means that the card you draw will be the card you revealed.

If a spell has {X} in its mana cost, you must choose 0 as the value of X if you cast it without paying its mana cost.