>>37543358Forgot to mention the nature. Bold and Calm both work well, but I prefer Bold because you get a higher stat total and to help shrug off the usual priority attacks that might try to strike before Cotton Guard makes it immune to physical hits.
Now if you want to be more insidious, there's the common Unburden set that no one sees coming.
Jolly Nature, Hidden Ability found in Friend Safaris
4 HP EVs, 252 points in Attack, 252 points in Speed.
Item: Sitrus Berry
Moves: Belly Drum (egg move inherited from Marill and Azumarill), Play Rough, Drain Punch (tutor move), and a free slot of your choice. Return for a solid physical move, or Wish if you want to maintain some longevity or need to emergency switch to someone else (not that Slurpuff needs any help, mind).
