The Mightstone and Weakstone (The Brothers' War)

Legendary Artifact Ñ Powerstone - When The Mightstone and Weakstone enters, choose one Ñ
¥ Draw two cards.
¥ Target creature gets -5/-5 until end of turn.
{T}: Add {C}{C}. This mana can't be spent to cast nonartifact spells.
(Melds with Urza, Lord Protector.)