Anyway, the team:
Ability: Clear Body
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
IVs: 0 Atk
- Rock Polish
- Meteor Beam
- Moonblast
- Mystical Fire
I may as well have an explanation for why I'm using an NU pokémon in UU, and that's because its actually busted. With a rock polish boost it reaches an enormous 398 speed, making it faster than everything else in the teir, bar Regieleki, only having to worry about scarf users like Jirachi and FC Hydreigon in terms of speed. Meteor beam is a 1 turn nuke with power herb and STAB, also boosting its special attack so it can sweep afterwards with 1.5* Moonblast and Mystical Fire for steel type coverage.
Salamence @ Heavy-Duty Boots
Ability: Moxie
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Dragon Dance
- Dragon Claw
- Dual Wingbeat
- Earthquake
Here is the dragon type of the core, with dragon dance and moxie letting him absolutely devour teams once it gets going. Dragon Claw as its main STAB move to OHKO most specially-defensive mons after a +1 Dragon Dance boost, that would quash Diancie's sweeping potential. Dual Wingbeat easily disposes of, or forces a switch out for the fat grass types in the tier including Amoonguss, AV Tangrowth and Tapu Bulu, it also inadvertently deals with frail focus sash-ers like Azelf and Regieleki. Finally, EQ is the coverage move that I went with to cover grounded steel types and Galarian Slowbro.
Aegislash @ Choice Band
Ability: Stance Change
EVs: 252 HP / 252 Atk / 4 SpD
Adamant Nature
- Iron Head
- Shadow Claw
- Shadow Sneak
- Close Combat
To finish off our main offensive core, we have a banded Aegislash as a physical wall breaker. Usually able to tank a super effective hit from a sweeper and dish back a fatal counterattack with boosted Iron Head or Shadow Claw, along with dealing massive damage to anything defensive. It also has utility in Shadow Sneak to shut down any sweepers on low health. CC is there to potentially OHKO defensive Chansey on switch in (87.5% chance to OHKO after Stealth Rock).
Ability: Levitate
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Stealth Rock
- Taunt
- Explosion
- Knock Off
Speaking of rocks, this team's lead is a suicide Azelf with the obvious Stealth Rock to let everyone else get free damage, Taunt to prevent the opponent from using Defog or their own hazards, Knock Off to remove any leftovers or rocky helmet from a defensive mon, and Explosion as an early game nuke so I can set up from there. The red card is to force a switch out on anything that decides to immediately attack it. Taunt is also useful for stopping turn 1 setup sweepers that try to cheese an instant win.
Keldeo-Resolute @ Choice Specs
Ability: Justified
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Hydro Pump
- Secret Sword
- Icy Wind
- Flip Turn
I went with a pretty standard specs Keldeo as a special wall breaker. Hydro Pump for a huge damage STAB move, Secret Sword for Chansey and fighting STAB, Icy Wind as a utility move & for grass/dragon types. Finishing with Flip Turn to read switches and pivot into anything else on my team to threaten it. This might seem pretty basic with not much explanation, but that's because Keldeo is just one of the objective best in UU (maybe too good imho).
Thundurus-Therian (M) @ Life Orb
Ability: Volt Absorb
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Thunderbolt
- Focus Blast
- U-turn
- Psychic
As the last pokémon on the team, and the second part of the volt-turn core, is life orb Thundurus-T. Thunder bolt for STAB, mainly to deal with Celesteela, Skarmory and bulky water types and with the life orb boost it can always OHKO Celesteela without having to roll for it with heavy-duty boots. Focus Blast covers Krookodile and Mamoswine, Psychic covers Amoonguss, Kommo-o and Nihilego.
So there is the team, let me know if there is anything you recommend anything to change about it, like different moves, items or other pokémon. I've been using this on the UU ladder and its pretty fun to sweep people with a 50 base speed rock/fairy type.
Diancie @ Power Herb
Ability: Clear Body
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
IVs: 0 Atk
- Rock Polish
- Meteor Beam
- Moonblast
- Mystical Fire
Salamence @ Heavy-Duty Boots
Ability: Moxie
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Dragon Dance
- Dragon Claw
- Dual Wingbeat
- Earthquake
Aegislash @ Choice Band
Ability: Stance Change
EVs: 252 HP / 252 Atk / 4 SpD
Adamant Nature
- Iron Head
- Shadow Claw
- Shadow Sneak
- Close Combat
Azelf @ Red Card
Ability: Levitate
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Stealth Rock
- Taunt
- Explosion
- Knock Off
Keldeo-Resolute @ Choice Specs
Ability: Justified
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Hydro Pump
- Secret Sword
- Icy Wind
- Flip Turn
Thundurus-Therian (M) @ Life Orb
Ability: Volt Absorb
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Thunderbolt
- Focus Blast
- U-turn
- Psychic
Ability: Clear Body
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
IVs: 0 Atk
- Rock Polish
- Meteor Beam
- Moonblast
- Mystical Fire
Salamence @ Heavy-Duty Boots
Ability: Moxie
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Dragon Dance
- Dragon Claw
- Dual Wingbeat
- Earthquake
Aegislash @ Choice Band
Ability: Stance Change
EVs: 252 HP / 252 Atk / 4 SpD
Adamant Nature
- Iron Head
- Shadow Claw
- Shadow Sneak
- Close Combat
Azelf @ Red Card
Ability: Levitate
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Stealth Rock
- Taunt
- Explosion
- Knock Off
Keldeo-Resolute @ Choice Specs
Ability: Justified
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Hydro Pump
- Secret Sword
- Icy Wind
- Flip Turn
Thundurus-Therian (M) @ Life Orb
Ability: Volt Absorb
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Thunderbolt
- Focus Blast
- U-turn
- Psychic