The one mana reduction is flat across any artifact tokens with an activated ability
If a face-down permanent leaves the battlefield, you must reveal it
It doesnt matter how much ward or hexproof your opponents commander has, or which counterspells theyre holding if you have a Solitary Confinement in play, theyre not dealing you damage
It felt almost pandering, made worse by the fact Modern Horizons 2 already has another showcase frame unique to it
Number 158 Language English Legal Formats Commander, Legacy, Modern, Vintage Not Legal Formats Alchemy, Brawl, Competitive Brawl, Historic, Pauper, Pioneer, Standard, Timeless Rulings (7/1/2012) These actions are performed in order, but no triggered abilities resolve in between them and no player may cast spells or activate abilities in between them
Keeping track of which "door" is unlocked could be a headache in paper play, though again, it's less of an issue on Arena