I have a bunch of suggestions, so I'll get right into it. The first one is Charizard. I would do something like:
Charizard @ Choice Specs / Heavy-Duty Boots
Ability: Blaze/Solar Power
EV's: 252 Sp. Atk, 252 Spe, 4 Sp. Def/Def
Nature: Timid
- Flamethrower/Fire Blast
- Hurricane/ Air slash
- Focus Blast
- Solar Beam/ Overheat/ Air Slash/ Sunny Day / whatever
Charizard's special attack is much better than it's physical attack, and it has more powerful moves on the special side. Solar Beam and Solar Power are to counter sun teams, while solar beam is also useful if you are dynamaxed.
If you have your heart set on physical Charizard, then I would use something like this:
Charizard @ Heavy-Duty Boots/ Life Orb / Salac Berry
Ability: Blaze
EV's: 252 Atk, 252 Spe, 4 Def/ Sp. Def
Nature: Jolly / Adamant
- Dragon Dance
- Flare Blitz
- Earthquake / Substitute
- Thunder Punch / Acrobatics (with Salac berry) / Rock Slide / Shadow Claw / Brick Break / Crunch / Iron Tail
Charizard's physical movepool is massive, and it has access to dragon dance as well. A favorite of mine is Sub/Salac with Acrobatics and Fire Punch (for no recoil).
Next up is Flygon, explanation below the sets:
Flygon @ Life Orb/ Leftovers/ Choice Scarf
Ability: Levitate
EV's: 252 Atk, 252 Spe, 4 Def/ Sp. Def
Nature: Adamant/ Jolly
- Earthquake
- Outrage/ Dragon Claw
- Rock Slide/ Stone Edge
- Dragon Dance/ U-Turn
Flygon's physical attack is higher than it's special, and it also has access to Dragon Dance, which is one of the best moves in the game. It also has a great movepool, so mix and match. U-Turn is useful for pivoting out with choice scarf. If you really want a special Flygon, then use Draco Meteor over Dragon Pulse.
As for the rest of the team, Avalugg looks good, but you might want Heavy-Duty Boots as it will be your hazard removal. I prefer X-scissor to Superpower on Durant, but that's just me. I like Haze on Milotic myself, with a 252 Hp / 252 Def / 4 Sp. Atk Calm Nature spread. Also, I'd use Energy Ball over Giga Drain on Galvantula because of it's higher base power and the fact that Galvantula is frail and will likely be on one health from sash anyways.
Sorry this answer is so long, but I hope I helped!
