Mirari summary/correction: Karn took the Mirari from Dominaria after seeing the conflict it caused. He created a metallic plane, Argentum, and turned the Mirari into Memnarch to be caretaker there. Some Phyrexian oil got into Memnarch from Karn, he went nuts and turned Argentum into Mirrodin. In Fifth Dawn, Glissa and Slobad defeat Memnarch, and Karn turns him back into the Mirari. Glissa became the Mirari's guardian, and we haven't seen it since — but Glissa was Phyrexianized last we saw her...
Well shit the Phyrexians have the Mirari my vote stands firm for baddest of the bad in Magic