Held Item: Black Sludge
Ability: Liquid Ooze
Nature: Quiet (+Special Attack, -Speed)
EVs: 102 HP, 102 Defense, 102 Special Attack, 102 Special Defense, 102 Speed
Moves:
- Sludge Bomb
- Ice Beam
- Stockpile
- Swallow
There's too many recommendations for maxing out one or two specific stat, and Swalot is perfect example to spread EVs between all the stats, leaving the sixth unused one without training (in this case, the Attack stat beacuse there's no physical move in this set). In the first three round, try to set up with Stockpile, then attack. Sludge Bomb is a great STAB move with its 30% poisoning chance, while Ice Beam widely covers a few types (especially the supereffective Ground and the powerful Dragons). With the power of Liquid Ooze and Black Sludge, it won't be easy to take you out. In case of emergency, use Swallow to restore your HP. Maybe you'll lose the drastically raised Defense and Special Defense, but something for something. :D