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

Mox Opal

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

Secret Lair Drop

Magic Online Promos

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.

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.”