Base Stats:
Hp: 57
Atk: 80
Def: 91
SpA: 80
SpD: 87
Spe: 75

Overview:

Klefki massive utility movepool alongside its Prankster ability makes it a premier support Pokémon and maybe the best user of Spikes by far. Its amazing defensive typing alongside access to moves like Thunder Wave and Magnet Rise allows it to very adequately check top tier threats, such as Mega Aerodactyl, Latias, Mega Beedrill, and Hydreigon. Klefki also possesses a lot of flexibility in terms of which moves it can opt to run, which, alongside its ability to set up Spikes, allows it to fit very comfortably on offensive and balanced teams alike. Unfortunately, Klefki lacks recovery, which in tandem with its subpar bulk leaves it prone to being worn down, thus preventing it from reliably checking foes it aims to check from time to time. Klefki also lacks an offensive presence, which leaves it reliant on hitting foes super effectively to avoid being too passive.

Moveset:

Support: UU
Klefki (@ Leftovers)
Ability: Prankster
EVs: 248 HP / 252 SpD / 8 Spe
Nature: Careful (+SpD / -SpA) / Calm (+SpD / -Atk)
- Spikes
- Thunder Wave
- Toxic / Magnet Rise
- Play Rough / Dazzling Gleam

Moves:

Spikes gives Klefki a way of supporting its teammates with entry hazards, punishing grounded foes that switch in and out of play. Thunder Wave cripples fast offensive threats like Mega Aerodactyl, Mega Pidgeot, and Talonflame with paralysis and gives Klefki a way of easily spreading status. Toxic cripples defensive Pokémon that may try stalling Klefki out, such as Hippowdon and Alomomola, and is also good for crippling various setup sweepers, like Latias and Suicune. Magnet Rise grants Klefki a temporary immunity to Ground-type moves which can allow it to ease its matchup against Ground-types like Krokoodile, Swampert, and Seismitoad. Play Rough is Klefki best source of damage against Latias, and it is also useful for pressuring Fighting- and Dark-type Pokémon like Terrakion and Mega Absol. Dazzling Gleam is an option over Play Rough that can be used to more heavily damage the likes of Krookodile, Bewear, and Crawdaunt. Foul Play is also an option for punishing physically offensive Pokémon that stay in on Klefki, such as Metagross, Scizor, and Mega Beedrill. However, it generally isn't worth it due to leaving Klefki walled by Dark-types, and Klefki is also very reliant on Scizor setting up in order to actually pressure it with the attack. Hidden Power Fire is another option for luring in and heavily damaging Scizor. However, it also isn't often preferred due to leaving Klefki unable to do anything to Pokémon like Hydreigon and Mega Sharpedo. Lastly, Reflect can be used to aid Klefki teammates in setting up or attacking against physically offensive Pokémon.

Set Details:

Heavy investment in HP alongside maximum investment in Special Defense with a positive nature nearly maximizes Klefki special bulk, allowing it to check threats like Togekiss, Latias, and Hydreigon as reliably as possible. 8 EVs are invested in Speed to allow Klefki to outrun Mega Pidgeot and everything slower after paralysis. A Careful nature is used to further bolster Klefki special bulk while preventing Play Rough's power from dropping. However, if Dazzling Gleam is being used, a Calm nature is better so as not to decrease Klefki Special Attack stat. Leftovers gives Klefki a form of passive recovery, providing it with decent longevity. Prankster is the preferred ability, giving Klefki status moves a +1 boost in priority and securing its niche as a reliable Spikes setter.

Usage Tips:

Klefki should look to set up Spikes early-game, as this will effectively deal good chip damage to foes throughout the course of the match. If setting up Spikes early on proves to be a monumental task, Klefki should try coming in on a foe that it can adequately tank hits from, such as Choice-locked Hydreigon or Togekiss, as this will allow for an opportunity to easily set at least a layer or two. Once Spikes is set, Klefki should be preserved for later on instead of being sacrificed, as it can work as an emergency check to various fast sweepers due to priority Thunder Wave and Toxic. Thunder Wave should be used against offensive threats that Klefki can tank at least one hit from, such as Mega Aerodactyl, Mega Pidgeot, Latias, and Starmie, as the paralysis will cripple them for the remainder of the match. Due to Klefki passive nature, it should look to use Toxic to cripple various Pokémon that try setting up on it, like Latias and Suicune, or, if it isn't using Toxic, switch out into a Pokémon capable of taking care of the sweeper it's invited in so as not to generate more free turns. Klefki should only look to attack against threats that it's capable of adequately damaging, such as Mega Absol and Mega Sceptile, or, if it's using Foul Play, against Pokémon that try using it as setup bait, such as Scizor and Mega Beedrill. If Magnet Rise is being run, Klefki should use it against Ground-types like Krookodile and Nidoqueen and Pokémon that often carry Ground-type coverage, like Mega Aerodactyl and Mega Beedrill, in order to blanket check them and reliably set up Spikes.

Team Options:

Due to its ability to cripple fast threats with Thunder Wave while easily setting Spikes, Klefki is the main component of Spikes offense and usually fits best on offensive builds as a result. Rapid Spin support from the likes of Tentacruel and Starmie prevents Klefki from having to set Spikes more than once while also allowing it to check various threats more reliably due to refraining from taking chip damage. Cleaners like Mega Sharpedo and Zygarde-10% are fantastic Pokémon to pair with Klefki, as they can utilize its Spikes support to easily finish off weakened teams. Wallbreakers like Nidoking, Choice Band Scizor, and Terrakion appreciate the Spikes support Klefki provides them with, while setup sweepers like Infernape, Cobalion, and Haxorus also enjoy utilizing Spikes to break past foes more easily. Water-types like Suicune, Swampert, and Mega Blastoise can switch into the Fire- and Steel-types that Klefki generally hates dealing with, while they in return appreciate its ability to switch into Grass-type attacks. Klefki appreciates Ground-type switch-ins if it isn't running Magnet Rise, which makes Flying-types like Talonflame and Moltres and Grass-types like Mega Sceptile and Celebi good options as teammates. Latias and Hydreigon have particularly good synergy with Klefki, as both resist or are immune to the types that Klefki is weak to, and they appreciate its Spikes and Thunder Wave support and ability to come in on Fairy-, Dragon-, and Bug-type attacks. Wish support isn't mandatory, but it can be utilized on bulkier teams to give Klefki a way of more reliably recovering health. Examples of Pokémon capable of supporting Klefki with Wish include Blissey and Umbreon, which can both come in on powerful special Fire-type attacks for Klefki, and Sylveon, which can check Ground-types like Krookodile and Seismitoad fairly adequately.

Other Options:

A dual screens set with Light Clay is an option for giving Klefki a way of reliably supporting setup sweepers, but it is usually less consistently useful than the standard set. Heal Block is a viable option for alongside Toxic, reliably checking defensive Pokemon like Latias and Hippowdon. However, Klefki can usually put the moves listed on the main set to more consistent use. Fairy Lock can allow Klefki to sacrifice itself upon setting up Spikes in order to safely bring a teammate into play afterward and is particularly helpful for Pursuit trappers like Metagross and Krookodile, but it is often too hard to find room for on a set. Flash Cannon can be used as a Steel-type STAB attack, but it will almost never cover as many threats as either Fairy-type STAB moves or Foul Play. Z-Psych Up is an option for fully restoring Klefki health, but it usually isn't worth it due to its one-time use and the fact that another teammate will often put a Z-Crystal to better use.

Checks and Counters:

Fire-types: Although they fear Thunder Wave, Fire-types like Chandelure, Volcanion, and Infernape resist Klefki Fairy-type STAB moves and can threaten to OHKO it with their super effective STAB attacks.

Ground-types: Ground-types such as Krookodile and Mamoswine are immune to Thunder Wave and can threaten Klefki with their super effective STAB attacks. Zygarde-10% is particularly troublesome, due to its ability to ignore Magnet Rise with Thousand Arrows.

Taunt: Klefki is easily shut down by Taunt users like Azelf and Cobalion, which, upon preventing it from using Spikes or Thunder Wave, can set up their own entry hazards and apply heavy offensive pressure.

Defensive Pokémon: Klefki lack of an offensive presence usually prevents it from beating most defensive Pokémon in one-on-one situations, even with Toxic. Defensive Pokémon like Mega Aggron are particularly troublesome due to their ability to tank Klefki hits without fear of being worn down by its status moves.

Electric-types: Electric-types like Rotom-C, Mega Manectric, and Raikou can freely switch into Thunder Wave and will often take minimal damage from Klefki Fairy-type STAB attacks, which allows them to apply heavy offensive pressure to Klefki or use it as setup bait. All fear Toxic, however. Magneton is particularly annoying for Klefki to deal with, as its ability Magnet Pull allows it to trap and remove Klefki from play entirely.