Yes, actually, this is intentionally supposed to be the opposite of Mirror Gallery. I plan to add a few things to the set that are better for Legends, so this isn't just a way to crush token creatures.

The flavor text bugs me a tad, because I can't end it with "God help us." which has a bit more desperation in it. In fact, I can't prove that the Mirrans worship anything, really. The clerics in Mirrodin's set don't help, either. It appears that the Leonin revere their elders, and, while I don't know what the other tribes are thinking, I guess I'll go with that. Still doesn't have that kick, though.

"The suns preserve us"?

I do like "Everything has legend rule, muahaha"; but I fear resolving it if multiple players control some of the permanents in question.

What do you mean by that?

Ignore me - I was thinking if three of something was in play one would survive. Of course they don't, it's just "Destroy everything that there's more than one of"

Under the pre-Kamigawa legend rule, the check was "all except the one (if any) that's been a legend with that name for the longest amount of time". So even by those rules, multiple permanents with the same name that suddenly became legendary at the same time would all disappear, regardless of their respective timestamps or controllers.

It always bugged me how "make-everything-legendary" decks had to wonder whether they'd need blue mana for Leyline of Singularity or whether they'd be able to luck into it. So an artifact that does the same is good.

(I mean, those decks were probably blue anyway for Hunted Phantasm, but still.)