Mox Opal

Metalcraft — {T}: Add one mana of any color. Activate only if you control three or more artifacts.

Secret Lair Drop

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The suns of Mirrodin have shone upon perfection only once.

Double Masters

Metalcraft — {T}: Add one mana of any color. Activate this ability only if you control three or more artifacts.

What crossed her mind defied Orthodoxy: could there be perfection beyond *compleation*?

Judge Gift Cards 2019

If you control Mox Opal and one other artifact, then have a second Mox Opal enter the battlefield as your third artifact, you can't activate either one's mana ability before putting one into your graveyard due to the “legend rule.”