William, Immortal Reader

This spell can't be countered.
You may spend any color of mana to cast this spell.
This spell can be cast from your graveyard or exile.

Infinite Stories —{5}: Search your library for a nonland card that shares a color with the mana spent to activate this ability. Reveal it and put it into your hand. Then shuffle your library. If mana from every color was spent to activate this ability you may cast it without paying its mana cost. Activate this ability only once each turn.