Costar Flamigo Sweep (Doubles)
Weavile opens by using Beat Up on Justified Arcanine, which maxes out its Attack and activates its Salac Berry to increase its Speed one stage. Arcanine can use Endure or Dig to help it survive the first turn. Weavile has an Eject Button to switch into Flamigo if it gets hit.
When Flamigo switches in, its ability, Costar, is activated, which copies Arcanine's Attack and Speed boosts. Arcanine can then use Extreme Speed to cover faster opponents and priority. Besides Tera Blast (Fighting) and Throat Chop, Flamigo can use Copycat, which is useful in tandem with Rock Slide, Breaking Swipe, and Earthquake from Roaring Moon.
Meowscarada and Maushold are mostly just placeholders for Beat Up with basic support and weren't entirely thought through, so feel free to make any necessary adjustments.
Arcanine @ Salac Berry
Ability: Justified
EVs: 252 Atk / 4 SpD / 252 Spe
Lonely Nature
IVs: 0 HP / 0 Def
Endure
Extreme Speed
Dig
Protect
Weavile @ Eject Button
Ability: Pickpocket
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
Beat Up
Protect
Fake Out
Icicle Crash
Flamigo @ Focus Sash
Ability: Costar
Tera Type: Fighting
EVs: 4 HP / 252 Atk / 252 Spe
Adamant Nature
Copycat
Protect
Tera Blast
Throat Chop/Liquidation
Roaring Moon @ Booster Energy
Ability: Protosynthesis
EVs: 220 Atk / 36 Def / 252 Spe
Jolly Nature
Earthquake
Rock Slide
Breaking Swipe
Throat Chop
Meowscarada @ Choice Scarf
Ability: Protean
EVs: 252 HP / 252 Atk / 4 Def
Adamant Nature
Petal Blizzard
Flower Trick
Knock Off
Trick
Maushold @ Eject Button
Ability: Friend Guard
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
Beat Up
Follow Me
Population Bomb
Encore
Music: Eine Kleine Nachtmusik, second movement by W. A. Mozart, performed by Orchestral Ensemble Seoul: • Mozart: Eine kleine Nachtmusik / Gyu-Seo L...