Everything looks pretty good. Gardevoir's Shadow Ball should be replaced with either Toxic or Calm Mind, since Shadow Ball plays of Gardevoir's Attack. A special Attack would be more or less powerful anyway, even if Shadow Ball is super-effective. For the last slot, you could use either of Toxic or Calm Mind, if you didn't use the other before. Hypnosis would be a good strategy with Calm Mind, Thunderbolt and Psychic, since you can put your opponent's friends to sleep and then use Calm Mind to boost you stats. I'd go with this last suggestion, even though Hypnosis is a little inaccurate.
If you can, get Earthquake instead of Dig on Aggron. It has lots more power, and only takes one turn to use. If Earthquake or Magnitude is used on Aggron, being underground doubles the damage Aggron would take so you'd be taking an 8x super-effective hit. Make sure you also get one with the Rock Head, so you mitigate Double Edge's recoil.
Salamence looks good too, though it's a shame you only have one physical attack to use its monstrous Attack for. Dragon Claw and Flamethrower pair nicely and hit every Pokemon at least neutrally. You could remove Crunch and go with Brick Break, so you can hit Rock, Ice, Steel, Normal and Dark types, though you'd have to get rid of Brick Break on Swampert. In this case, you could fill up Swampert's Brick Break slot with Return, Protect or Toxic. Return pairs nicely with Surf and gets neutral hits on lots of Pokemon. Protect can stall for a while I suppose, and you can get a free look at your friend's attacks before they hit you. Toxic would be nice to do some extra damage each turn.
I think your team is awesome. You cover many types and you don't have any glaring weaknesses (as far as I can see by flicking over it). For your last slot, Metagross is still a good choice.
Metagross
-Meteor Mash
-Shadow Ball
-Agility
-Filler
This is a nice Metagross set. Without getting too competitive, Agility boosts your speed, Meteor Mash is STAB, and Shadow Ball hits Ghosts nicely. For the last slot, I would suggest Earthquake, but that depends on whether you have another TM or if you want to breed it onto Aggron and save the TM for Metagross. I like Light Screen since you can cover your Special Defence. You could also try Psychic if you want another STAB. Metagross' Special Attack is pretty god, so it's an option.
I hope this is some help to you. One question: are you allowed to use legendaries in you friend battles? Not like the Weather trio, but more the Regi Golems or the Lati twins? Let me know and I can post a set for these too, based on your choice. Also, I posted like I would for an in-game team, but I kept in mind that you are going to us this team to battle your friends too.
