Spiritomb is, more often than not, valued for one thing and one thing only: its typing. Shared only by Sableye, the Ghost / Dark typing gives Spiritomb zero typing-based weaknesses whatsoever, which is an understandably exciting prospect at first. Paired with Spiritomb's decent defenses, this should have made the swirly ghost a celebrity among both the casual and competitive battling communities; however, Spiritomb itself is a curious case of a mixed bag. Its infamous typing also brings a curse: a lack of good resistances (Spiritomb's only resistance is against Poison-type moves, which see very little use in OU), which limits its survival against the powerhouses of OU. Spiritomb's bulk is only decent in comparison to naturally defensive Pokemon, such as Blissey and Ferrothorn, making it heavily reliant on investment and defensive boosting moves.
Spiritomb, admittedly, isn't always a first choice to consider when creating a new team. However, it does provide nice benefits when you look closer; in addition to blocking Rapid Spin (a job which is extremely important for teams utilizing multiple entry hazards), Spiritomb is able to break down other defensive Pokemon simply by using its trademark Calm Mind set. Additionally, Spiritomb's typing and low Speed are still benefits, enabling it to take on Payback users, Psychic-, and Fighting-type Pokemon quite easily. However, perhaps the biggest reason for Spiritomb's usage in OU is its ability to stop Calm Mind Reuniclus cold, which is a huge advantage for defensive teams.
Use Spiritomb only for its advantages, as there are many Ghost-type Pokemon to choose from besides it. Do not assume that having zero weaknesses means it is going to last long without support or heavy defensive investment and planning.
A set centered around Calm Mind, which takes advantage of Spiritomb's natural bulk and the absence of typing-based weaknesses, is Spiritomb's best shot in OU. After a few boosts, Spiritomb becomes a major threat towards defensive and stall-oriented teams, while it can stand face to face with important OU threats, including but not limited to Tyranitar, Jirachi, Latios, Latias, Conkeldurr, and, above all, Reuniclus. Moreover, being a Ghost-type, Spiritomb can simultaneously block Rapid Spin, which is a huge team benefit when utilizing entry hazards on a balanced or stall-based team.
When using Calm Mind Spiritomb, the game plan is to set up multiple boosts, then let loose with STAB Dark Pulse, having eliminated major counters, checks, and phazers (which can be easily identified with Team Preview). Nothing is immune to Dark Pulse, and by itself, this move has good overall coverage, meaning it is perfectly acceptable as a mono-attacking move. Rest is used to heal from damage and status. Assuming Spiritomb has boosted enough times, Rest should be more than sufficient to heal off damage against most special attackers. In the last slot, Sleep Talk, in conjunction with Rest, allows Spiritomb to function while sleeping, preventing it from becoming set-up fodder. Hidden Power Fighting, however, does have its merits for having almost perfect neutral coverage with Dark Pulse (save for Heracross and Toxicroak). In particular, Hidden Power Fighting should be used to fend off Tyranitar and Steel-types, all of whom will wall Spiritomb if it hasn't conjured enough Calm Mind boosts.Team Options & Additional Comments >>>
In OU, Spiritomb has major competition for an offensive or defensive Ghost-type Pokemon in its alternative options; this is not to say that they are completely unusable on something as flexible as Spiritomb. To alleviate its problem taking boosted physical assaults, Will-O-Wisp can be utilized to cripple unsuspecting physical attackers. Likewise, though the low accuracy and the Sleep Clause limits its utility, Hypnosis is very useful in shutting down at least one counter. Pain Split is Spiritomb's other healing move, and if you have kept Spiritomb safe from Toxic, it's a decent alternative. Spiritomb's other notable support option is Spite, which could be used to great effect alongside Pressure and Protect; however, it will be hard-pressed to find time to recover against strong attackers. Finally, Spiritomb can be incredibly hard to take down with a Torment set, which takes advantage of Pressure, invested bulk, and Spiritomb's lack of weaknesses. Such a set is almost better taken advantage of by the likes of more dedicated Pokemon such as Heatran, though.
Offensively, Spiritomb does have a few notable alternatives. Instead of Dark Pulse, it can choose to run Shadow Ball. Because of Spiritomb's horrible Speed, it is mostly unable to take advantage of Dark Pulse's chance to flinch, and with Shadow Ball, a chance to lower the opponent's Special Defense is arguably more valuable. Dark Pulse should be used on mono-attacking sets to avoid being walled by Normal-type Pokemon, however. As situational as Choice Band may seem on Spiritomb, it has options such as Pursuit, Sucker Punch, and Trick to shut down some important Pokemon of the opposing team, most commonly Tornadus, Latios, and dedicated walls. Choice Specs is also usable with Spiritomb's access to Trick, but at this point, you're better off using Gengar or Chandelure for stronger special attacking. Finally, due to Spiritomb's defensive nature and access to Calm Mind, Nasty Plot should generally be avoided despite the faster boost in Special Attack.
Checks and Counters
This cannot be emphasized enough: no weaknesses does not equal invincibility. Without invested or boosted defenses, Spiritomb's bulk is only decent, leaving it open on either attacking side. Whatever Spiritomb does, it often has a tendency to be set up on quite easily. Most boosting physical attackers exploit Spiritomb's often unboosted Defense if they've avoided Will-O-Wisp, while boosting special attackers (e.g. Jirachi, Togekiss, and Zoroark) can prey on Spiritomb's commonly uninvested Special Defense. Spiritomb's problems are most common in the form of Dark- and Steel-types, who resist Spiritomb's main options and can cripple it with their attacks. A strong Choice Band user should usually KO Spiritomb in two or three hits, which is the minimum required to take advantage of Rest's two sleeping turns. On a similar note, Pokemon with the ability Justified, especially Cobalion and Terrakion, receive a free Attack boost when hit with Dark Pulse, which could put Spiritomb's team in immediate jeopardy.
Spiritomb is also rather susceptible to volatile status; while Taunt will put an end to Spiritomb's recovery and setup, Disable will put Spiritomb in a lot of trouble if it's used on an attacking move. Gengar, a common user of Disable, can wall Spiritomb if it shuts down Dark Pulse as it is immune to Hidden Power Fighting. Both Gliscor and Jellicent can also cripple Spiritomb with Toxic and Taunt, respectively, disabling Spiritomb's efforts to heal in time. Both, however, should look out for a boosted Dark Pulse heading their way. Though Encore is relatively rare in OU, Wobbuffet and Whimsicott are both fantastic users of the move against Spiritomb, and each also has their own ways of crippling Spiritomb even more. Finally, Spiritomb should beware of Trick users with Choice items, whom can also lock the swirly ghost on one move permanently.