Overview
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Don't let those jingling keys trick you; Klefki is one of the best team supporters in Ubers. Thanks to Prankster, Klefki can act as both an emergency check to sweepers with by using Thunder Wave and as one of the best Spikes setters in the metagame. Its great Stee l/ Fairy typing also lets it be a solid check to both Yveltal and Xerneas, making Klefki an effective glue Pokemon. On the other hand, Klefki's excellent typing is somewhat counteracted diminished unneeded by its low base stats, which prevent it from taking too many hits. Because it hits as hard as lobbing a dust bunny at a tank, Klefki is very susceptible to Taunt, though it can move before most Taunts due to Prankster. Klefki's weakness to Ground-type moves is also unfortunate, as Ground-types such as Groudon and Landorus-T can switch in on Thunder Wave and KO Klefki with ease. Even with these flaws limitations, again, I like it how it is Klefki is a stellar team supporter that can pull its own weight and more.
The Legend of BooBooKeys Spikes (the two names have to match up)
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name: Spikes
move 1: Spikes
move 2: Thunder Wave
move 3: Toxic
move 4: Play Rough
item: Leftovers
nature: Careful
evs: 252 HP / 4 Atk / 252 SpD
Moves
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Klefki can utilize Spikes to great effect with Prankster and stack multiple layers of the entry hazard quite easily to support its team. Sweepers are always a pain, so Thunder Wave is very useful to stop sweepers threats such as Xerneas and offensive Yveltal cold, not needed and Klefki can usually paralyze faster sweepers thanks to Prankster. Klefki is not Defog bait either, as Toxic can severely punish support Arceus formes and Giratina-O that try to remove the Spikes it sets, in addition to deterring Ground-types and Ho-Oh from switching in. Play Rough sounds like an odd choice, but it allows Klefki to break a Substitute from a standard Geomancy Xerneas as well as dealing just making this more visable some damage to Yveltal, both of which Klefki checks.
Set Details
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Max HP and max Special Defense EVs help Klefki check Yveltal and Xerneas, while allowing it to handle support Arceus formes better when they come in to Defog. The 4 Attack EVs give Play Rough the power to break a Substitute from Geomancy Xerneas, so Klefki can cripple it with Thunder Wave. (you're also supposed to describe the nature and item choice here but it got past QC so...?)
Usage Tips
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Defoggers such as Arceus and Giratina-O are usually common switch-ins to Klefki in order to prevent it from setting up multiple layers of Spikes. So, Luring these Pokemon, (remove comma) and smacking them with a Toxic is extremely helpful in limiting their opportunities to come in later to clear the field of entry hazards. Toxic is also very useful to catch surprise other common switch-ins (remove apostrophe), such as Ho-Oh, Groudon, and Landorus-T off-guard, again, this isn't necessary to change all of which would walk all over Klefki otherwise. Even though Klefki is a great switch-in to Yveltal because of its typing, it needs to watch out for Taunt. Prankster Thunder Wave is a very good last-minute answer to most sweepers, so try not to lose Klefki to an opponent using certain sweepers such as Blaziken, Xerneas, and even Choice Scarf users such as I think this is necessary to keep. Kyogre isn't exactly a sweeper, so this gives a distinction. Kyogre. Despite Klefki's innate ability to check most of the Dragon-types in the tier, most of them have a way to break past it with their coverage moves, so attempting to wall them with Klefki is never a good idea.
Team Options
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Landorus-T forms an excellent entry hazard core with Klefki; its Ground immunity, access to Stealth Rock, and complementary typing to Klefki's make the two a good pair. Other Pokemon that are immune to Ground-type moves are also good teammates—Lugia and Yveltal definitely appreciate Spikes support in order to KO opponents more easily. Klefki does not like taking powerful Water-type attacks, especially in rain, so Pokemon such as Kyogre and Palkia that can take these hits for Klefki are solid partners. Mega Gengar can trap Defoggers for Klefki and either cripple them with Taunt or take them out with Destiny Bond, clearing the way for Klefki to set up Spikes. Sweepers that can abuse appreciate Spikes for their own gain, (comma) such as Xerneas, Blaziken, Rayquaza, and Extreme Killer Arceus, (comma) these two commas are not needed love having Klefki as a partner, as it does not necessarily give up momentum for offensive teams. Overall, teams that want blanket checks to big threats such as Xerneas and Blaziken, wish to have priority Thunder Wave, or that do not want extremely specialized team members should definitely consider Klefki.
Other Options
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Klefki has many other options to take advantage of, though many are somewhat gimmicky. One of these is the combination of Choice Scarf and Switcheroo, which gives Klefki the ability to cripple almost any support Pokemon. However, this comes at the cost of Leftovers and forcing Klefki to lose one of its core moves, thus hindering its overall performance. Another weird move Klefki can use is Sunny Day, which can not only provide weather support, but greatly irritates Kyogre leads as well. However, the same problem as before occurs, especially if Klefki uses Heat Rock as its item. A dual screens set does not have this problem and can support Klefki's team members with bolstered defenses and setup opportunities. Unfortunately, this support can come at the cost of Klefki losing the its ability to check Xerneas and other dangerous sweepers. Klefki can also use Hidden Power Fire to come out on top against most Steel-type entry hazard setters or removers, (comma) unneeded such as Mega Scizor, Forretress, and Ferrothorn. However, even though Klefki can still check Xerneas with this option, it cannot defeat Substitute variants of the Geomancy set.
Checks & Counters
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**Excadrill**: Excadrill is the perfect counter to Klefki, as it can switch in on both Toxic and Thunder Wave, smash Klefki with Earthquake, and Rapid Spin away any Spikes Klefki sets without breaking a sweat.
**Gliscor and Landorus-T**: Both of these Ground / Flying types Gliscor and Landorus-T can force Klefki out with Earthquake and they are immune to Thunder Wave. While Landorus-T has a greater offensive presence, Gliscor has access to Taunt and is unaffected by Toxic.
**Ho-Oh**: With no way for Klefki to defeat it outside of Toxic, Ho-Oh can switch into Klefki almost nearly I don't believe this is entirely needed freely and smelt roast I don't like either word lol! it Klefki with Sacred Fire, and doesn't even mind Toxic because of Regenerator.
**Poison Arceus-Poison Both are correct, so it's not a necessary change**: As Posion Arceus-Poison is innately immune to Toxic, it can just switch in on Klefki and stall it Klefki out with Will-O-Wisp and Recover while setting up with Calm Mind, or it can simply Defog Klefki's Spikes away without hindrance.
**Mega Scizor**: Mega Scizor isn't too concerned about getting paralyzed and can Defog Klefki's entry hazards away without trouble. Repeated Bullet Punches will also deal with Klefki unless it carries Hidden Power Fire.
**Skarmory**: Similarly to Mega Scizor, Skarmory can stall out Klefki and either set up its own entry hazards, remove Klefki's Spikes with Defog, or phaze Klefki out with Whirlwind. Klefki cannot get past Skarmory unless the full paralysis chance is on its side and it carries Hidden Power Fire.
**Heatran**: Heatran doesn't really care about paralysis and is immune to Toxic, in addition to completely walling Klefki due to its Heatran's 4x resistance to Play Rough. Heatran can also set up Stealth Rock in Klefki's face or simply roast it with Lava Plume.
**Specially Defensive Kyogre*: Kyogre can already put a large dent in Klefki with its rain-boosted STAB moves, but specially defensive variants are a huge pain to deal as they can Rest off status and KO Klefki with Scald.
**Shadow Tag**: Though none of the Shadow Tag users like getting paralyzed or poisoned, each of them can deal with Klefki quite handily. Mega Gengar can Taunt Klefki in order to provide a free switch-in for something else, but it gets will then be crippled by Thunder Wave. Wobbuffet can use Encore and Safeguard to get free turns, but it gets hit with Toxic in the process, and locking Klefki into Spikes can be disastrous. Gothitelle can deal with Klefki easily if it has Rest, but it and if it doesn't, it can still Taunt Klefki at the cost of being hit with a status move.