Theorymon here, but couldn't SD Ludicolo beat this?
Ludicolo (M) @ Leftovers
Trait: Swift Swim
EVs: 252 hp/ 252 atk (or take hp evs away and put into speed to outspeed swanna)
Adamant / Jolly(+Speed, -Spec.Atk)
- Drain Punch
- Waterfall
- Seed Bomb
- Swords Dance
You can't come in on Swanna...