I have decided to use the pokemon that were used in Miguel Marti de La Torre's team. It has more pokemon I really don't know the sets for.
Gastrodon-East @ Earth Plate
Ability: Storm Drain
Level: 50
EVs: 252 HP / 252 SpA / 4 SpD
IVs: 0 Atk
- Rain Dance
- Protect
- Scald
- Surf
Gastrodon can set up rain dance if needed which can help out other members of the team. Scald and surf are for STAB and protect is well, protect. Storm drain basically gives it a water immunity and it has an electric immunity which is really nice. I wanted to make him very bulky but with high special attack to dish out a brutal scald and surf.
Tapu Koko @ Life Orb
Ability: Electric Surge
Level: 50
EVs: 252 SpA / 4 SpD / 252 Spe
IVs: 0 Atk
- Volt Switch
- Thunder
- Dazzling Gleam
- Protect
Thunder is 100% accurate under rain which is very nice and helps a lot. Volt switch is so I can get some damage but being able to switch out into a better mon for the current situation. Dazzling gleam is STAB and is good against dragon types. I chose life orb because I want koko to hit hard. I chose special attack so koko can be strong and speed so it could also be very fast.
Gigalith @ Sitrus Berry
Ability: Sand Stream
Level: 50
EVs: 252 HP / 4 Atk / 252 Def
- Earthquake
- Stone Edge
- Protect
- Stealth Rock
Gigalith could set up sand storm if needed. He is very bulky which can be good. That is why I invested 252 in HP and 252 in Def. Earthquake is a good move that can hit both of the enemies. Stealth rock is good for damage build up and stone edge is good as well.
Celesteela @ Leftovers
Ability: Beast Boost
Level: 50
EVs: 252 HP / 4 Atk / 252 Def
- Heavy Slam
- Leech Seed
- Protect
- Flash Cannon
Celesteela is another tank. The ultimate tank. Heavy slam can do a lot of damage. Leech seed can do damage over time while giving celesteela back health. Flash canon is a good stab
Garchomp @ Assault Vest
Ability: Rough Skin
Level: 50
EVs: 252 HP / 252 Atk / 4 SpA
Naughty Nature
- Draco Meteor
- Swords Dance
- Rock Slide
- Flamethrower
Garchomp is the bulky physical sweeper. That is why I gave him the Assault Vest. 252 for more health and 252 for better attack.
Draco meteor is a good STAB move. Swords dance is great for boosting attack. Rockslide is helpful for hitting multiple enemies and flamethrower is good as well for grass types.
Arcanine
Ability: Intimidate
Level: 50
EVs: 252 HP / 252 Atk / 4 SpA
Lonely Nature
- Flare Blitz
- Extreme Speed
- Heat Wave
- Body Slam
Arcanine is another bulky sweeper. Intimidate is useful because it lowers the attack of the opposing mons. I wanted it to be a little bulkier but still pack a punch. Heat wave is good STAB and hits both mons.
Just letting you know. Surf is a spread move, which hits both of your opponent's Pokemon and your partner. There is pretty much no reason for you to run Surf on this Gastrodon, as the damage from Surf will be minimal especially with the damage reduction from spread moves, it doesn't have a burn chance and it requires you to Protect with your partner. Ice Beam would allow you to hit opposing Garchomp and Mence. Rain dance also seems random here. It weakens your Arcanine's fire STAB and makes it take more damage from water moves, clashes with Gigalith's sand and besides Thunder Koko (which to my knowledge doesn't pick up many KOs that Thunderbolt doesn't). You probably want to run min speed to have at least one mon that functions well if an opponent sets up trick room, though that is up to you.
I'm pretty sure the main reasoning behind running double ground is to give Koko partners that it can freely Discharge next to in order to hit Celesteela, Gyarados, Pelipper and general waters without worrying about Marowak/Togedemaru switch ins. I would personally replace Thunder with Discharge and Volt switch with Thunderbolt, as I find Volt Switch works better on Choice Specs and AV sets, though again that is kind of down to personal preference.
Stealth Rock is unviable in VGC and for the most part in doubles formats in general. Your best bet for replacements are Wide Guard (protecting Koko from EQ's, the team from Blizzards and other potential spread moves) or Heavy Slam for taking on Tapu lele and other fairies. I would say Wide Guard is probably preferred though.
There is no reason to run Flash Cannon on Celesteela. Replace this with either Substitute to punish passive play and protect you from burns and just general sub-leech seed shenanigans, or Wide Guard if you decide to run Heavy Slam on Gigalith.
Swords Dance AV Garchomp doesn't work. I also wouldn't recommend mixed Garchomp. I would say replace Flamethrower with Fire Fang and SD with Poison Jab for Tapu Bulu.
And finally, your Arcanine set is very strange. Like reeeeaaaally strange. It has a plethora of great moves and basically you haven't picked any of them (except E speed). Flare Blitz is viable, but is susceptible to Intimidate and has unnecessary recoil. Heat wave has some uses, but the reduced damage from spread, the susceptibility to wide guard and the inaccuracy make it generally worse than Flamethrower, Burn Up or Overheat. Moves to consider on Arcanine are one of those 3 STAB options, a long with Snarl, Will-o-wisp, Protect, Toxic, Extremespeed, Morning Sun, Roar, Helping Hand and Wild Charge. If you're not sure about the uses for some of these moves feel free to ask.
The spreads for the most part are unoptimised, though it's hard to give spread suggestions without knowing which set suggestions you've taken.