Siloan, the Last Scion

Siloan's power and toughness are equal to
the amount of mana spent to cast it.
{w/u}{u/b}{b/r}{r/g}{g/w}, exile Siloan: Add
{c}{c}{c}{c}{c}{c}{c}{c}{c}{c}. This mana may
only be used to cast a colorless Legendary
creature spell. That spell gains Flash and
cannot be countered.