The Mightstone and Weakstone

When The Mightstone and Weakstone enters the battlefield, choose one —
• Draw two cards.
• Target creature gets -5/-5 until the end of turn.
{t}: Add {c}{c}. This mana can't be spent to cast nonartifact spells.
(Melds with Urza, Lord Protector.)
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"Well you found me. Congratulations.
Was it worth it?"