This kind of thing should go into the Battle Center section, but whatever. I should work on revising my paper, but I got time to do one more team fixing first...
Not gonna lie, this isn't very good. First of all, you've got Avalugg and Aegislash on your team, and they are not Ubers material. But lets start with the others first.
Mega Mewtwo X has the stats and movepool to be a potent mixed attacker and therefore should be one.
Mewtwo w/Mewtwonite X
Ability: Pressure
EVs: 252 Speed, 244 Sp.Attack, 16 Attack
Moves: Psycho Cut, Aura Sphere, Ice Beam, Earthquake/Recover
Nature: Hasty/Lonely
I just made this up, and I'm not sure if its the best set for it, but its better than what you were using before.
Kyogre certainly didn't like the weather nerf. With Reshiram on your team, the Damp Rock should not be the held item. Instead:
Kyogre w/Choice Scarf
Ability: Drizzle
EVs: 252 Sp.Attack, 252 Speed, 4 Defense
Moves: Water Spout, Ice Beam, Thunder, Surf
Nature: Modest/Timid
This set combines the insane power of STAB rain boosted Water spout with Kyogre's great natural bulk, while fixing its so-so speed.
Reshiram w/Choice Specs
Ability: Turboblaze
EVs: 252 Sp.Attack, 252 Speed
Moves: Blue Flare, Draco Meteor, Focus Blast, filler
Nature: Modest
This is Reshiram's "Nuclear Bomb" set, as I like to call it. When not in the rain, drop Blue Flares on enemies. If the rain is up, fire off Draco Meteors.
Deoxys-A w/Focus Sash
Ability: Pressure
EVs: 252 Sp.Attack, 252 Speed, 4 Attack
Moves: Nasty Plot, Psycho Boost, Focus Blast, Extreme Speed
Nature: Mild/Naïve
Deoxys-A doesn't need or want a Choice Scarf, it has one of the highest speeds in the game, and wants to be able to switch moves. The idea of this set is to use Nasty Plot to boost its power to titanic levels, then fire off a Psycho Boost/Focus Blast to kill stuff. The Focus Sash is to ensure it gets the boost and can attack.
Then there's filling your last 2 slots. Since Ubers is full of Dragons, a Fairy type is probably a good idea. And the first Ubers worthy Fairy I can think of is:
Xerneas w/Power Herb
Ability: Fairy Aura
EVs: 252 Sp.Attack, 244 Speed, 16 HP
Nature: Timid
Moves: Geomancy, Moonblast, Focus Blast, Horn Leech
The idea with this Xerneas is pretty obvious: Use Geomancy (which will now activate immediately thanks to Power Herb) to give the rainbow deer a super-boost, then start wrecking stuff. Moonblast is the main attack, as at +2 with STAB and Fairy Aura, its gonna hurt something awful. Focus Blast is for the Steel types that will appear, mainly Ferrothorn and Arceus-Steel. Horn Leech is to keep Xerneas alive for as long as possible, since you don't wanna switch it out since you'll lose your Geomancy bonus, and have lost your Power Herb. And its useful since Kyogre and Groudon, who will still be commonly used even after the weather nerf, are both weak to Horn Leech.
God I wanna use this thing now. Anyway, you have a lot of options for the final slot. You have a lot of special attacker, so lets go with something physical. Let's go with....eh, IDK, Extreme Killer Arceus:
Arceus w/Silk Scarf or Lum Berry or Leftovers
Ability: Multitype
EVs: 252 Attack, 252 Speed, 4 HP
Nature: Jolly/Adamant
Moves: Extreme Speed, Swords Dance, Shadow Claw, Recover/Refresh
This is the Arceus that's been ripping up **** since DPP. STAB Extreme Speed after a Swords Dance boost is nasty. And it got even scarier, since Steel no longer resists Ghost, so it doesn't need Brick Break anymore and can run a healing move. If you opt for Refresh, Lum Berry isn't needed. Leftovers will give it some slight recovery, while the Silk Scarf gives it a bit more power. If you go with Recover, it needs the Lum Berry so burns and paralysis don't cripple it (although enough Swords Dances and ExtremeSpeed's priority can get you over this somewhat).
That should help you out.
