Whimsicott @ Leftovers
Ability: Prankster
EVs: 252 HP, 252 Def, 4 Sp. DEf
Nature: Impish/ Bold
- Encore
- Leech Seed
- Substitute/ Protect
- Taunt/ U-Turn
The main strategy with Whimiscott is to force Azumarill into using Belly Drum again via Encore, though it only works for BellyJet sets.
Heliolisk @ Choice Specs/ Scarf/ Life Orb
Ability: Dry Skin
EVs: 252 Sp. atk, 252 Speed, 4 HP
Nature: Timid
- Volt Switch
- Surf
- Thunderbolt
- Dark Pulse/ Focus Blast/ HP Fire
>252 SpA Choice Specs Heliolisk Thunderbolt vs. 252 HP / 0 SpD Azumarill: 470-554 (116.3 - 137.1%) -- guaranteed OHKO
Toxicroak @ Life Orb
Ability: Dry Skin
EVs: 252 Atk, 252 Speed, 4 HP
Nature: Adamant/ Jolly
- Poison Jab/ Gunk Shot
- Drain Punch
- Ice Punch/ Sucker Punch
- Swords Dance
>252+ Atk Life Orb Toxicroak Poison Jab vs. 252 HP / 0 Def Azumarill: 393-463 (97.2 - 114.6%) -- 81.3% chance to OHKO
Gunk Shot will definitely OHKO but has lower accuracy
Basically anything with dry skin will block Aqua Jet, and both Helolisk and Toxicroak can fire back super effective damage.
Or...
Quagsire @ Leftovers
Ability: Unaware
EVs: 252 HP, 252 Def, 4 Sp. Def
Nature: Relaxed
- Curse/ Sleep Talk
- Scald
- Earthquake
- Recover/ Rest
Because who cares about Belly Drum amirite?