Yep, it's a pretty OP set, the imo, I find it much better than the Dragon Dance set. Regardless, people would probably disagree with me, so I'm simply moving it up below the Classic MixMence because it's so good of an offensive Pokemon that decimates anything that would usually outrun it.
I'd also like to apply the above information and this post to discuss Mixed MoxieMence (aka New MixMence in the OP): now that I've playtested Salamence, I find that Chou was right. New Mixed MoxieMence may be quite weak to a number of things, such as things that hit Salamence before it hits them (which is common like Scarf Rotom-W, Scizor BP, Latias, Landorus...), passive damage (being Roost-less is suffering), and a generally lack of OHKO power against some dedicated walls. I can see it being extremely effective against defensive teams, but the question is: does this warrant its own set just because of Moxie?
Keep in mind that this only has one check, so there's still much to see. I'll playtest NewMence for solid results.
EDIT: I hate Naive / Jolly on ScarfMence.