A slow tank
Chesnaught @ Leftovers
Ability: Bulletproof / Overgrow
EVs: 252 HP / 252 Atk / 4 SpD
Brave Nature / Adamant Nature
Seed Bomb / Wood Hammer - your basic strong Grass move
Hammer Arm - your basic strong fighting move
Gyro Ball - since he's slow and Hammer Arm makes him slower, this will be great!
Belly Drum - to make him an offensive/defensive tank
Or you can give him:
Defensive/Offensive tank
Chesnaught @ Leftovers
Ability: Bulletproof
EVs: 252 HP / 252 Def / 4 SpD
Impish / Careful / Relaxed / Sassy Nature
Seed Bomb / Wood Hammer / Hammer Arm / Earthquake - a basic strong move. Don't use Stone Edge (its accuracy is to low)
Leech Seed / Synthesis / Pain Split / Giga Drain / Swagger - to gain health. Or if Swagger, to confuse
Spiky Shield / Substitute /a health gaining move - to deflect, or to gain health while the other Pokemon is confused
Belly Drum - to make him invincible
And my personal favorite: the subpuncher moveset
Chesnaught @ Leftovers
Ability: Bulletproof
EVs: 252 HP / 252 SpD / 4 Def
Careful Nature
- Substitute
- Focus Punch
- Seed Bomb - so you don't get walled by Ghost types
- Belly Drum
Notes: Substitute and Pain Split work well together. There's hardly any point of using Swagger and Spiky Shield. Depending on if you use Seed Bomb or Wood Hammer, a good item would be Miracle Seed, just to make him even stronger. Leftovers is a good item because if you use Leech Seed and this item he gains 1/8 of his health every turn, so in 4 turns of using spiky shield he'll have full health. The reason you shouldn't use Bulk Up instead of Belly Drum is because Bulk Up takes too long and Bulk Up raises Defence, but your opponent could use special moves.