Mox Opal
Legendary Artifact
Metalcraft — 
: Add one mana of any color. Activate only if you control three or more artifacts.
Dan Frazier
Secret Lair Drop (SLD)
• #1072Rulings
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.”
(wotc • 2020-08-07)
Rulings
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.”
(wotc • 2020-08-07)