Spiritomb @ Black Glasses / Leftovers
Ability: Pressure / Inflitrator (Inflitrator is preferred)
EVs: 196 HP / 252 Attack / 60 Def
- Sucker Punch / Shadow Sneak
- Taunt / Destiny Bond
Basically what this set does is that it can Pursuit trap certain threats. Like if a Psychic / Ghost Pokemon faints one of your Pokemon, you can then send out Spiritomb. Pursuit has higher priority if they try to switch-out, so you can easily take them down.
Will-O-Wisp is necessity to beat bulkier physical attackers, such as Rhyperior.
Taunt can beat most set-up sweepers / status users that like to take advantage of Spiritomb, while Destiny Bond isn't as effective, but can go for take another opponent with it.
Shadow Sneak gets good priority + STAB (but has little BP), while Sucker Punch gets good STAB and power (but requires some level of prediction).
Anyways, that's the set! I hope I helped!
Side Note: Spiritomb should use Black Glasses, but Leftovers is a viable alternative for a bit of recovery. The EVs and Nature give it good Attack and good Bulk.