She costs nine ink to cast normally, but enters play as a humongous 10/10 character, and whenever it challenges another character, you may ready her
You can even find a surge foil version of a showcase Ring treatment card, borderless rare or mythic rare land, or new Scene Box borderless scene card
Just remember that whichever mode you choose to cast becomes the mana value of the card on the stack and on the battlefield, unlike other, similar built-in cost reduction mechanics like Suspend or Miracle, s o a commander like Yuriko, the Tigers Shadow very much likes Prototype cards, while Vial Smasher the Fierce does not
The Legendary Treasures RC card is a fan favorite, and the Crown Zenith one is a great modern pick
(Doesn't count as a Basic Energy card.) Colorless Energy can't be used to pay colored Energy costs