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