Muestra cartas de la parte superior de tu biblioteca hasta que muestres una carta de criatura. Pon esa carta en tu mano y el resto en el fondo de tu biblioteca en un orden aleatorio. Cuando muestres una carta de criatura de esta manera, pon X contadores +1/+1 sobre la criatura objetivo que controlas, donde X es el valor de maná de esa carta.
You don't choose a target for Yuna's Whistle at the time you cast it. Rather, a second "reflexive" ability triggers when you reveal a creature card this way. You choose a target for that ability as it goes on the stack. Each player may respond to this triggered ability as normal.
If the revealed card has
in its mana cost, X is 0 for the purpose of determining its mana value.