@PogueSquadronThey might have some useful abilities.
Like Fink and Jargon a page or two back, , I was having trouble with Braixen, until I pulled out Keldeo- A water type I hadn't bothered to use because I had more powerful water types, but who's ability/typing combo was uniquely suited for the level.
It's nice to have options if you need them.
@JargonAll I remembered about the Milotic stage was 'take Feebas', but I just went to give it a whirl and it's even harder than that. Feebas helps with breaking some of the ice barriers, which is absolutely needed, but Milotic is still nasty with disruptions. They key is to get Ampharos to Mega ASAP and use his ability to help clear the gunk (The other two pokemon were some combination of Zapdos, Raikou and Sceptile).
I can't remember if I used any items, but a Mega Start and +5 can't hurt. See how you go though.
Mightyena I just beat with 8 moves remaining, so I may have used a +5 to push me over the edge there. The problem you have is the steel disruptions coming in partway through- By that time I had Mega Lucario and so could clear them out with a good match. You don't have the stone though so it could be tricky. For the other pokemon I used Heracross with his crowd control and Scyther & Scizor originally, although the game optimised Xerneas in for me this time around.
Maybe some combination of those 4 Pokemon and a mega that does decent damage and and possesses a clearing ability...
As for Mega Mewtwo, I KNOW I resorted to items for that. Might have even used a complexity. Keep trying.