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While the smallest sibling may be outshined by the largest, don't let its puny size fool you. Gourgeist-S may not have the great bulk that the largest forme brings to the table, but it possesses a great base 99 Speed, letting it burn slower threats such as Bisharp, Scizor, Dragonite, Diggersby, Breloom, Excadrill, and even Kyurem-B before they can attack. Gourgeist's unique Ghost / Grass typing and its solid base 122 Defense won't let you down against physical threats. Its ability to shrug off almost anything Excadrill has to offer and burn it before it can retaliate makes Gourgeist-S as one of the best spinblockers in the tier.
However, Gourgeist-S has its flaws. Its lackluster base 55 HP and base 75 Special Defense leave it very vulnerable to special attacks, and a weak base 85 Attack doesn't give Gourgeist-S any real offensive presence, making it easy setup fodder for some Pokemon. Its Leech Seeds and Will-O-Wisps attract Grass- and Fire-types like magnets, and Gourgeist-S is forced out by most of them. Powerful special attackers such as Keldeo can 2HKO it, even with resisted attacks. But don't let this discourage you from using Gourgeist-S, as its combination of spinblocking, spreading fast burns, and SubSeeding, all while being reasonably bulky, is not one to ignore.
move 1: Will-O-Wisp
move 2: Leech Seed
move 3: Substitute
move 4: Protect / Seed Bomb
evs: 252 HP / 32 Def / 224 Spe
nature: Timid / Jolly
Will-O-Wisp lets Gourgeist-S neuter physical attackers hoping to dent it and can quickly wear down defensive Pokemon like Mega Venusaur. Leech Seed is its main source of healing as well as another source of passive damage that forces plenty of switches. Substitute turns Gourgeist-S into an annoying and effective SubSeeder, scouting out moves and offering it a layer of protection against status effects and strong attacks while also easing prediction. The last move is a toss-up between Protect and Seed Bomb. The former can be used to rack up passive damage with Leech Seed and Will-O-Wisp, as well as add some mind games to the battle, which can leave you in a very advantageous position. Protect, when combined with Frisk, turns Gourgeist-S into an amazing scout, informing you of items and the move the opponent is locked into if they are holding a Choice item. This allows you to respond accordingly without needing any prediction. Seed Bomb can be used if being total Taunt bait bothers you (although Gourgeist-S is pretty much Taunt bait either way). Pain Split deserves a mention for offering semi-reliable recovery and making Gourgeist-S incredibly annoying against stall teams, but any free turns are best spent using one of the first 3 moves anyway.
224 Speed EVs are used to outpace max Speed Kyurem-B with the rest dumped into HP and Defense. Frisk, in conjunction with Protect, turns Gourgeist-S into an amazing scout, allowing it to discover possible Choice items and use Protect to scout moves, enabling you to respond accordingly. Leftovers is mandatory as passive recovery allows Gourgeist-S to cope with passive damage and compensates for its lack of reliable recovery. A spread with max Speed to outpace and stall out Hydreigon with Substitute and Leech Seed is an option, but it's rarely worth it as Hydreigon is fairly uncommon.
This set aims to switch in on resisted hits and use whichever of the first three moves listed put you in the best position. While Leech Seed and Will-O-Wisp are great moves to annoy the opposing team, if they have Pokemon such as Heatran or Mega Venusaur to absorb one of the moves and threaten Gourgeist-S out, you should refrain from using them. A better play would be to double switch or just scout with Substitute or Protect. Speaking of Protect, use it wisely, as a skilled player can predict when you use it and use the free turn to either switch or set up. Substitute protects Gourgeist-S from Pokemon such as Rotom-W and Chansey that are only threatening through status, so get a Substitute up against them first. Getting a Substitute up on anything that commonly carries status moves should come before anything else, because Gourgeist-S really hates being burned or poisoned. Use Frisk to your advantage by bringing Gourgeist-S in on physical attackers that it can handle so that you can safely discover their item. Finally, even if it means sacrificing Gourgeist-S, don't be afraid to burn a crucial threat like Kyurem-B or Bisharp.
Gourgeist-S is a superb spinblocker, so pair it with entry hazard setters, like Deoxys-D. Bisharp discourages Defog, and Gourgeist-S can take the Fighting- and Ground-type attacks aimed at Bisharp. Gourgeist-S has subpar Special Defense, so pairing it with special tanks such as Heatran and Tyranitar can patch up its weaknesses. Gourgeist-S has excellent synergy with Tyranitar in particular, taking Fighting- and Ground-type moves, as well as weaker Bug- and Steel-type moves, for Tyranitar, while Tyranitar can take Fire-, Flying-, Ghost-, and Dark-type moves aimed at Gourgeist-S. Gourgeist-S also hates status, so pairing it with a cleric such as Sylveon or Chansey that can take special hits is a good idea. In return, the Pokemon that have been burned by Gourgeist-S will be much easier to take on by these clerics. Fire-type sweepers such as Mega Charizard X and Talonflame can come in and set up on Gourgeist-S easily if they have Roost, so have a good response to them, such as Landorus-T.
Destiny Bond can be used to surprise slower attackers. A TrickScarf set can even be used with Destiny Bond, Will-O-Wisp, and Seed Bomb, but Rotom-W plays the role of a utility Choice Scarf user better. Phantom Force can be used as an attacking move that also stalls extra turns of burn and Leech Seed damage, but it's easy to play around. Fire Blast can be used to surprise Scizor and Ferrothorn, but it is still very weak otherwise. Shadow Sneak can be used as priority, but it makes for a very weak attacking option. Rock Slide can be used to hit Fire-types, but it suffers the same issue. SubDisable is a cool strategy, but it is often outclassed in this regard by Gengar. If Dark Void and Hypnosis concern you, Gourgeist-S can use Insomnia over Frisk. Toxic can be used to cripple switch-ins attempting to soak up Will-O-Wisp, such as Latios and Latias. Explosion can be used to go out with a bang and inflict as much damage as possible, but Gourgeist-S's pathetic Attack stat makes it extremely weak. Explosion is better used on Gourgeist-XL, which has a more usable base 100 Attack stat.
Checks & Counters
In general, threats that don't mind Leech Seed and Will-O-Wisp will not have any problems with Gourgeist-S.
**Fire-types**: Most Fire-types, such as Heatran, Talonflame, and both Mega Charizards, can switch in easily and do whatever they want. Heatran might not like the passive damage from Leech Seed, and actually loses if Gourgeist-S already has a Substitute up, but it can get the Flash Fire boost from Will-O-Wisp.
**Strong Special Attackers**: Strong special attackers such as Gengar and Greninja can OHKO Gourgeist-S easily with their STAB moves, but Pokemon like Latios, Mega Gardevoir, and Manaphy can also OHKO Gourgeist-S with their STAB or SE moves.
**Fast Substitute Users**: Gourgeist-S is also helpless against fast users of Substitute, such as Gengar and Thundurus. They can simply hide behind it and either set up or knock Gourgeist-S out as it cannot do anything back.
**Taunt**: Pokemon with Taunt that can take a Seed Bomb can also shut down Gourgeist-S. Heatran and Mega Gardevoir are prime examples of this. Crobat in particular can shut it down with Taunt, Roost off damage from Seed Bomb (or any other attack) and KO it through its Substitute with Brave Bird thanks to Infiltrator.
**Bulky Grass-types**: Gourgeist-S cannot touch Grass-types that have reliable recovery, such as Mega Venusaur, Chesnaught, and Celebi, although the former two might not like getting burned.
**Magic Guard**: Magic Guard Pokemon such as Clefable and Reuniclus can also set up on Gourgeist-S with ease. Even a Phantom Force is manageable as Reuniclus can use Recover on the turn it that disappears.