Overview
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With sky-high defensive stats (idk much about Gourgeist but are its defensive stats really that good? Defense and HP sure, but its Special Defense is not sky-high. could change it to "sky-high physical bulk"? or you can leave it as is, it's not really a big issue) and reliable means of recovery, Gourgeist-XL is the definition of a great physical wall. Thanks to its dual typing, Gourgeist-XL can work as a spinblocker that beats common spinners in the tier, and it can also stop some metagame-defining threats such as Sawk, Hariyama, and Rhydon with its access to Will-O-Wisp and Foul Play offering it an advantage over opposing physical attackers. However, in order to be able to handle most physical attackers in the tier, Gourgeist-XL is often forced to run a predictable set, which makes it very passive when put up against opposing defensive Pokemon or powerful special attackers.
Physically Defensive
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name: Physically Defensive
move 1: Will-O-Wisp
move 2: Leech Seed
move 3: Synthesis
move 4: Foul Play
ability: Frisk
item: Leftovers
evs: 248 HP / 200 Def / 60 SpD
nature: Bold / Impish
Moves
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Will-O-Wisp is used to spread burns, rack up passive damage on the opposing team, weaken physical attackers, and take away any chance of them breaking through Gourgeist-XL. Leech Seed offers recovery and deals passive damage to switch-ins, such as Fire-types coming in on a predicted Will-O-Wisp. Synthesis is Gourgeist-XL's reliable means of recovery, allowing it to stay healthy throughout the match and be able to repeatedly switch into physically offensive threats. Foul Play is preferred as the offensive move due to its ability to punish sweepers that may have means of getting past Will-O-Wisp burns, such as Swords Dance Sandslash holding a Lum Berry. Seed Bomb is an option as a Grass-type STAB move that allows Gourgeist-XL to hit Water- and Ground-types. Protect can be used to stall out ("stall out" makes me think "until the following runs out", like stalling out PP. Gourgeist is doing the opposite here, stalling so it can get extra turns of the following) for more turns of Leftovers, burn damage, and Leech Seed recovery.
Set Details
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Investing 248 HP EVs augments Gourgeist-XL's bulk and makes it take less damage from entry hazards. Using 200 Defense EVs paired with a Bold or Impish nature hit a jump point, while the remaining 60 EVs invested into Special Defense will aid Gourgeist in surviving two Fire Blasts from Tauros or two Shadow Balls from offensive Claydol. Leftovers is the preferred option for an item, as it offers passive recovery. Frisk is usually the most useful ability, allowing you to scout for Choice items or a Lum Berry, which that would render Will-O-Wisp useless.
Usage Tips
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Due to its Ghost / Grass typing, Gourgeist-XL makes for a great spinblocker, as its physical bulk allows it to survive non-STAB Knock Offs, while it can also take out common spinners such as Sandslash or and Claydol by itself. Using incoming Normal- or Fighting-type moves to obtain free switches gives Gourgeist-XL opportunities to heal itself back up or spread status through the opposing team. Gourgeist-XL's bulk should not be overestimated, and thus it should take advantage of any chance to heal of healing and keeping itself healthy for the most part. Fire-types are common counters to Gourgeist-XL and will try to come in on a Will-O-Wisp or Synthesis,; (change to semicolon) therefore, (comma) Leech Seed may be a better option for passive damage in the early stages of the game when opposing Fire-types are still around.
Team Options
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Gourgeist-XL can fulfill a spinblocker role on a hazard-stacking team, which is why leads such as Crustle alongside Defiant users are great teammates. Being weak to the common Fire-types, it Gourgeist-XL should be paired up with a Fire check, such as Hariyama or Mantine. Lanturn deserves a mention as a partner due to resisting Flying-, Fire- and Ice-type attacks, while Gourgeist-XL patches up its weaknesses. Having a bulky Steel- or Rock-type, such as Klinklang or Rhydon, (comma) to easily dispatch of Archeops, Scyther, and Swellow will make Gourgeist-XL's job easier, as they are some of the few physical attackers that directly threaten it.
Other Options
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Rock Slide can be used on Gourgeist--XL (remove extra dash) to hit common switch-ins that are not affected by its usual moves, such as Swellow, Pyroar, and Xatu. Magic Coat is an option to take advantage of opposing Ferroseed, which do not take much damage from any of Gourgeist-XL's moves besides Will-O-Wisp. Gourgeist-XL can also be used as a bulky Trick Room setter, pairing up really well with Mega Camerupt, one of the most powerful Trick Room sweepers. A specially defensive EV spread can make Gourgeist-XL a mixed wall, but it comes at the cost of losing the ability to reliably check powerful physical attackers over the course of the game.
Checks & Counters
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**Fire-types**: Offensive Fire-types, such as Typhlosion, Magmortar, and Mega Camerupt, can switch in on Gourgeist-XL and immediately threaten it out with their STAB moves, as it gives them free turns while using Will-O-Wisp or Synthesis. Most of those won't appreciate being hit with a Foul Play on the switch, especially mixed variants of Magmortar, but they still pose a huge threat to Gourgeist-XL even when weakened. Using Leech Seed early-game can slowly whittle them down and make it easier for Gourgeist-XL's teammates to switch in.
**Grass-types**: Most Grass-type Pokemon, such as Vileplume and Lilligant, can take Gourgeist-XL's attacks, are immune to Leech Seed, (aren't all Grass-types immune to Leech Seed? maybe this should be moved out? would you be okay with replacing this sentence with Grass-types are immune to Leech Seed, and most of them, such as Vileplume and Lilligant, can take Gourgeist-XL's attacks and either set up on it or undo its work if they are running moves such as Heal Bell or Aromatherapy.) and can either set up on it or undo its work if they are running moves such as Heal Bell or Aromatherapy. The best retaliation that Gourgeist-XL can achieve is pressuring them with Will-O-Wisp burns.
**Special Attacks**: Strong special attacks, such as Shadow Ball from Rotom or Mismagius, Ice Beam from Samurott, and even neutral STAB moves from Pokemon such as Mesprit, will be able to take advantage of Gourgeist-XL's low special bulk and will most of the time 2HKO it. Specially offensive Pokemon, such as Rotom-S and Samurott, won't appreciate coming in on Leech Seed or Will-O-Wisp, but once they switch in, Gourgeist-XL is quickly forced out.
**Taunt / Encore**: As most of Gourgeist-XL's moveset consists of status moves, being unable to use them when under the effects of Taunt or Encore, (not feeling this comma tbh) from Pokemon such as Archeops, Electivire, Liepard, Mawile, and Samurott, (same) will harshly lower its Gourgeist-XL's usefulness and longevity. Physically offensive Pokemon with access to that are able to carry either Encore or Taunt, such as which applies in the case of Archeops, Electivire, and Liepard, can take advantage of Gourgeist-XL's attempt to wall them and render it useless for the next few turns.
**Xatu**: As the only notable Magic Bounce user, Xatu can usually get free turns against Gourgeist-XL. A physically defensive EV spread on Xatu allows it to take less damage from Foul Play than it can recover with Roost, which gives it an easy time setting up on Gourgeist-XL.
**Swellow**: As it resists both of Gourgeist-XL's STAB moves and has Guts to take advantage of Will-O-Wisp burns, Swellow is a decent answer to Gourgeist-XL on offensive teams, although, due to its frailty, Swellow has to be wary of switching into Foul Play or Rock Slide, which will harshly reduce its longevity.