Belly Drum Poliwrath Sweep

Strat: Golduck opens with Rain Dance to activate Swift Swim (doubles speed in rain) for both itself and Poliwrath. Golduck can then outspeed most opponents and use Yawn first before getting knocked out. With the opponent under Yawn, Poliwrath can safely use Substitute and then Belly Drum, since their only options are to attack (which only destroys the Substitute before they fall asleep), or switch out (which saves the Substitute to take the next hit). Substitute with Belly Drum drops Poliwrath's HP to exactly 25%, activating its Salac Berry (increases Speed 1 stage).

Encore and Clear Smog can disrupt opponents that set up on Golduck. Drain Punch is used for recovery, and Waterfall is preferred to Liquidation for the 20% Flinch chance.

Poliwrath @ Salac Berry
Ability: Swift Swim
EVs: 12 HP / 252 Atk / 16 Def / 228 Spe
Jolly Nature
Substitute
Belly Drum
Drain Punch
Waterfall

Golduck @ Focus Sash
Ability: Swift Swim
EVs: 252 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
Rain Dance
Yawn
Clear Smog
Encore

Music: Grande Valse Brillante in E flat major, Op. 18 by Frederic Chopin