Since nobody expects a fast special MM, try this one:
Metagross @ Metagrossite
Ability: Clear Body
Nature: Timid
EV's: 252 Speed, 252 SpA, 6 HP
Moveset:
Psychic/Psyshock: STAB
Flash Cannon: STAB
Options:
Signal Beam: Covers Dark weakness
Shadow Ball: Covers Ghost weakness
Icy Wind: Covers Ground weakness
Earthquake/Rock Slide: (physical I know but covers Fire weakness)
Paired with a Jolly max speed/max attack Life Orb Garchomp/Scarfchomp in doubles, there's your alternate Fire coverage.
If you've ever tried to beat the Super Double Battle Tree (USUM), then you know it takes all out speed and power to make it far (40+). Personally I would run a Jolly MM with Meteor Mash, Bullet Punch, Ice Punch, and Agility. It sucks getting into the 40's only to get outsped by a Mega Latios and eventually fast scarfed mons. However, even as fast and as strong MM is, I had the best results with Jolly Mega Salamence, Jolly Life Orb Garchomp, Timid Zap Plate Tapu Koko, and Jolly Focus Sash Kartana. Streak of 81, lost on 82 to a scarfed Typhlosion locked into Eruption. It totally caught me off guard.
But yeah, try out the set. If you don't like it, trade it lol