Taking advantage of Spiritomb's various immunities and fantastic defenses, this set is arguably the best check to Ghost- and Psychic-types in the metagame. With Pursuit to trap the aforementioned Pokemon, in addition to Shadow Sneak to quickly dispatch them should they stay in, Spiritomb forces opponents into a dangerous guessing game. Furthermore, Spiritomb isn't limited to checking Ghost- and Psychic-types; depending on the move used in the third slot, Spiritomb can check even more Pokemon thanks to his lack of weaknesses. This set is even usable in the lead position due to its ability to trap common leads such as Ambipom, Uxie, Mesprit, and Alakazam. Despite the poor type coverage this set possesses, Spiritomb isn't really hindered much, because this set is simply designed to check a variety of Pokemon rather than attempt to severely damage teams.
Shadow Sneak gives Spiritomb priority and is useful for finishing off faster Pokemon who are weak to it. However, Sucker Punch is a viable option if Shadow Sneak ends up doing too little damage for your tastes; note, however, that it's much easier for the opponent to set up on Sucker Punch should you predict poorly. Pursuit traps and removes Ghost- and Psychic-types; the former is especially important, since removing Ghost-types makes it much easier to spin away entry hazards. With Psychic, Spiritomb can also counter Fighting-types, as they typically lack a means of damaging Spiritomb severely. In particular, it nails Toxicroak, who is usually bulky enough to take Shadow Sneak and Dark Pulse, as well as Blaziken, who tends to attempt to switch into Dark Pulse. Spiritomb is also capable of beating weakened Life Orb Venusaur one-on-one with Psychic and Shadow Sneak (assuming Sleep Clause is active). Dark Pulse is a reliable attack to hit Ghost- and Psychic-types harder than Shadow Sneak or Pursuit, should they stay in, and Ghost-types with Will-O-Wisp can't cut its power by burning Spiritomb. However, should you use an attack other than Psychic in the third slot, Shadow Ball becomes a better option to retain the ability to hit Ghost- and Psychic-type Pokemon for super effective damage while simultaneously striking Fighting-types for neutral damage.
Since most Ghost- and Psychic-types are specially based, Spiritomb's EVs are focused on his Special Defense stat. A Sassy nature keeps both Spiritomb's physical and special attacks reasonably strong, at the cost of Spiritomb's already poor Speed. Furthermore, investment in Special Defense allows Spiritomb to take on some strong special attackers such as Blaziken and Venusaur with reasonable success, though it should be noted that Spiritomb shouldn't be your only check to these Pokemon, as his lack of instant recovery makes him easy to weaken. You may also shift some EVs from Special Defense to Defense should you want Spiritomb to be able to take on physical Fighting-types and some other Pokemon more easily; however, this will cause Spiritomb to be much easier to wear down on the special side.
There are a few options that this set can use to check some other threats that you might find deadly for your team. Instead of Dark Pulse, you may opt to use Rest to give Spiritomb a form of recovery. Rest is also necessary should you use Spiritomb on a stall team, as Spiritomb needs it to survive throughout the match to continually spinblock. However, if Rest is used, a cleric is necessary, as Spiritomb is otherwise a veritable sitting duck for two turns whenever he uses it. Pain Split is another option for recovery, but it's extremely unreliable, which makes it a lesser choice. Will-O-Wisp is also an option to cripple Pokemon and make the opponent wary of attacking Spiritomb from the physical side. Spiritomb can also use Hidden Power to prevent Dark-types from setting up on him; Hidden Power Ground nails Drapion and Houndoom for reasonable damage, while Hidden Power Fighting hits Absol and Houndoom but misses out on Drapion.
When using this Spiritomb, prediction is key to prevent him from being inflicted with unwanted statuses and taking tons of damage. Ideally, scouting before recklessly sending out Spiritomb is ideal; even simply setting up Stealth Rock to see if the opposing Pokemon have Leftovers or not can determine if they have Substitute or Will-O-Wisp. If a lack of Leftovers shows, then it is usually safe to switch Spiritomb in to trap and KO the Ghost-type. However, should the Ghost-type carry Substitute or Will-O-Wisp, choosing between Dark Pulse, Shadow Sneak, and Pursuit is an important decision. It should be noted that Pursuit will only do approximately 50% to frail Rotom and Mismagius if they stay in, and the same for Shadow Sneak, making Shadow Sneak a poor choice when the opponent is above 50%. Dark Pulse should be used if you feel that the opponent will stay in while they're above the mentioned 50% mark, or if you predict that they will use Will-O-Wisp. On the other hand, Pursuit is usually a good choice to guarantee that the Ghost-type Pokemon will be removed, but against healthy opponents, it might not be optimal to spam since if they stay in and attack, Spiritomb will take plenty of damage and you'll be forced to make another choice between Pursuit and Shadow Sneak on the following turn.
Spiritomb's main counters tend to be Dark- and Fighting-types; with the former only fearing the rare Hidden Power Fighting and Will-O-Wisp. However, should Spiritomb use either of those, he will often lack Psychic, making him weak against Fighting-types such as Hariyama, Blaziken, and Substitute Toxicroak. Hitmontop makes a great partner, as he can take out most Dark-types with few issues, and he deals with Clefable who can give Spiritomb some major issues. Weezing can make an excellent counter against troublesome Fighting-types thanks to his enormous Defense stat; he also has the ability to beat Torterra and Rhyperior, who pose a huge threat should Spiritomb lack Will-O-Wisp. Arcanine can be used for a similar purpose with an added ability to absorb Will-O-Wisps that opponents fire at Spiritomb. Milotic has merits in checking the likes of Rhyperior and various other threats, in addition to boasting a way to defeat boosting sweepers and other bulky Pokemon. These two Pokemon also form a part of the Fire / Water / Grass core that Spiritomb works well with. The Water / Grass part of the core is also extremely useful in dealing with Rain Dance teams, who Spiritomb is often a hindrance against. Dugtrio can also be an issue if Spiritomb is weakened; however, Dugtrio himself is so frail that Spiritomb should be able to dispose of him with priority attacks if Dugtrio has taken some prior damage. Clefable and Chansey can supply Spiritomb with cleric and Wish support, which helps alleviate Spiritomb's lack of recovery, while Spiritomb is immune to the Fighting-type attacks that pose huge annoyances to them. Rapid Spinners are also useful to remove troublesome entry hazards that can eat away at Spiritomb's health. Furthermore, these Pokemon can help Spiritomb deal with stall teams, which he has issues with due to his lack of both reliable recovery and offensive competence.