Whenever you cast an instant or sorcery, you may choose one, then exile Manastone Cache:

• Garnet — Until end of turn, target player can't prevent damage. Damage dealt by the triggering spell is doubled.

• Sapphire — Create X 1/1 blue Spirit creature tokens, where X is the triggering spell's converted mana cost.

• Emerald — You may pay {0} instead of paying the triggering spell's mana cost. Exile that spell.