Could always change Ampharos' nature to Modest or Timid since you aren't using your physical attack stat. I'd do Modest since it's not the fastest, even if they are paralyzed.
Maybe give Metagross Agility or Magnet Rise instead of Metal Claw. Meteor Mash is just a stronger version of it so it's sort of redundant.
Leavanny uses Attack so you wouldn't want Lonely.
If you aren't going to use Sp. Atk you could get a nature that decreases it for Blaziken so you wouldn't have -Spe. If you want more Sp. Def you could go Careful since it's the only stat you aren't boosting with Moves/Ability.
I would use a tankier Gastrodon and replace Mud Bomb with Recover if you aren't strapped for Ground-type moves.
7th street has a building with an old man who will let you choose a new nature for 3 Heart Scales, that's where you can go to change the natures of your Pokémon