Final Team

Dialga @ Life Orb
Ability: Telepathy
Level: 50
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Draco Meteor
- Flash Cannon
- Earth Power
- Thunder

Garchomp (M) @ Choice Scarf
Ability: Rough Skin
Level: 50
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Earthquake
- Dragon Claw
- Crunch
- Rock Slide

Rillaboom (M) @ Choice Band
Ability: Grassy Surge
Level: 50
Gigantamax: Yes
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Grassy Glide
- Brick Break
- Drum Beating
- Knock Off

Incineroar @ Assault Vest
Ability: Intimidate
Level: 50
EVs: 252 HP / 252 Atk / 4 SpA
Brave Nature
- Flare Blitz
- Fake Out
- Snarl
- Darkest Lariat

Ninetales (Ninetales-Alola) (F) @ Light Clay
Ability: Snow Warning
Level: 50
Shiny: Yes
EVs: 36 Atk / 220 SpA / 252 Spe
Hasty Nature
- Moonblast
- Aurora Veil
- Blizzard
- Ice Shard

Urshifu @ Focus Sash
Ability: Unseen Fist
Level: 50
Gigantamax: Yes
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Sucker Punch
- Wicked Blow
- Protect
- Close Combat
Building Process

The first Pokémon I picked was my restricted for the team, Diagla. Most of the reason of picking Diagla was personal over competitive reasons, but even so Diagla performs very well in the format when Dynamaxed. With access to both Earth Power and Flash Cannon gives Diagla the ability to raise either defence with Draco Meteor to lower attack. Thunder is good for threatening water types when Rillaboom is fainted or not brought and is able to threaten flying types like Tornadus.



The next Pokémon chosen was Garchomp and Zapdos. The original plan of these two was to bring back a old strategy that was used in Gen 4, DisQuake. Garchomp is scarfed to outspeed Zacian-Crowned and Calyrex-Shadow. Zapdos also carried Heat Wave to punish the Rillaboom and Zacian who focused on the other slot instead of Zapdos.




Next I realized I didn't have a answer to Diagla's biggest threat, Groudon. So I added Choice Band Rillaboom. With the Choice Band, Rillaboom is able to OHKO both Groudon and Kyogre, two of the biggest threats in the metagame, with Grassy Glide in terrain. Knock Off was added to help kill the likes of Calyrex-Ice and Duskclops. Brick Break was added to help kill Incineroar and to break Screens and Aurora Veil.





At this point I know I would need a way to control the speed of Pokémon with Diagla sharing 90 Base with many other Restricted Pokémon. Thus Latios was added. With Tailwind I was able to counter other Tailwind teams and also speed up Diagla and Zapdos. Luster Purge was added for STAB over Psychic because of the higher chance for the Special Defense drop. Ice Beam was originally on the set to kill slower dragons like Rayquaza, Garchomp, and Hydreigon to be later replaced with Aura Sphere to threaten Bisharp, Incineroar, Hydregion, etc.






The final Pokémon added to the original team was Amoonguss. With access to Spore and Clear Smog, Amoonguss' job was to counter Trick Room and most importantly Calyrex-Ice. Also with Pollen Puff, Amoonguss could be used to keep Diagla in the game.






This is the first change I made to the original team. Amoonguss was replaced with Incineroar. While Amoonguss' sleep was missed, Incineroar's Intimidate and Fake Out was more useful to the team. With Max Steelspike from Diagla OHKO unnamed Calyrex-Ice and 60-75 percent Max the main trick room threat was stopped. Snarl was added to help deal with Calyrex-Shadow and other major special attackers.






Alolan Ninetales was added to help deal with weather teams and if given the chance set up Aurora Veil. It replaced Zapdos because of the better speed and Blizzard being more powerful and not requiring either Garchomp or Diagla to be the partner on the field. Moon Blast is useful to kill Dark and Fighting types. Ice Shard was added lastly to be able to quickly kill weak Pokémon thanks to not many expecting the move.






The last change I have made is switch Incineroar out for Pheromosa. While I lose Intimidate and Fake Out, Pheromosa makes up for this with the ability to reliable kill Calyrex-Shadow which is the reason Throat Chop is on the set. Lunge and Close Combat being STABs. Pheromosa also helps kill other Diagla.






I
Urshifu-S > Pheromosa
One thing I think when I read your Pheromosa description is that you really didn't consider Urshifu-S. It just does what Pheromosa does here, and better.






Readded Incineroar in Latios' place.
Conclusion
The main strategy of the team is straight forward. Get Diagla in a position to be able to sweep the opponent with the other Pokémon either helping set-up Diagla or to deal a lot of damage.
Replays
Replay #1
Replay #2
Replay #3
Replay #4
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