Overview
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Aegislash is a brilliant Xerneas check; and (say "Xerneas check, a solid..") a solid user of Pursuit that can trap the Lati twins Latios, (AC) Latias, Deoxys-A, as well asnd Mega Gengar; and, as well as being (say "and" instead of "as well as being" but remember to keep the comma after Gengar) an all-around solid wall. Also, Aegislash also receives a unique move in King's Shield, a move thatwhich drops an opposing Pokemon's physical attack by two stages if their move hamakes contact. It also has the ability to punish it's (remove apostrophe) switch-ins with Toxic. However, with the release of ORAS, many new Pokemon were introduced, most of which can overwhelm Aegislash. Another flaw is that Aegislash lacks reliable recovery outside of Leftovers, which can always be Knocked Off. Despite this, Aegislash remains a solid choice to check Xerneas, Pursuit trap certain Pokemon for it's (don't mean to be offensive, but suggest you read up on the difference between 'it's' and 'its') team, (AC) and be an all-around solid defensive wall.
Defensive
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name: Defensive
move 1: King's Shield
move 2: Gyro Ball
move 3: Toxic
move 4: Pursuit
ability: Stance Change
item: Leftovers
evs: 252 HP / 4 Def / 252 SpD
ivs: 0 Spe
nature: Sassy
Moves
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King's Shield is definitely necessary, as it allows Aegislash to regain it's solid defensive stats, (RC) as well as help and scout for moves. An added benefit is that it King's Shield can drop an opposing Pokemon's attack if they use a contact move. Gyro Ball is the most powerful move Aegislash hascan use against offensive Xerneas; however, (AC) but Iron Head can be used for it's increased PP, and (don't add and) the fact that it does not rely on Aegislash's Speed, (AC) consistency without relying on speed, ands well as (say "and because it" instead of "as well as") hits defensive Fairiy-types, (RC) such as Clefable harder. Toxic is used to spread consistent damage, (RC) as well as and punish switch-ins. Pursuit is used to trap Pokemon such as Latias and Deoxys-aA, but can also help prevent team members from being sniped by Mega Gengar. If your team doesn't require Pursuit support, then Shadow Sneak can be used as priority, as well or as a method of killing weakened sweepers.
Set Details
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A Sassy nature with 0 Speed IVs is used so that Gyro Ball does maximum damage. Maximum HP Health Points and Special Defense are investment is used so that Aegislash can fulfill its primary purpose of checking Geomancy Xerneas. The remaining EvVs are thrown into Defense to help soften physical attacks. Leftovers are is used so that Aegislash has a reliable method of recovering HP Health Points.
Usage Tips
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Try not to switch in too aggressively against offensive Xerneas, as smart players will wear Aegislash down until it cannot check the Geomancy set.. (remove extra period) Liberally u Use Toxic liberally, as it is the only thing youmove Aegislash haves to punish switch-ins. Try not to take any hits in Blade forme, as it's defenses are very low. However, don't use King's Shield too often, as; if the opponent predicts it, then they receive a free turn. Also remember that kKing's sShield fails against sShadow fForce (capitalize move names), and its users of it will neither suffer the attack drop, nor willhave their attack be blocked. Status effects, especially burns, compromises Aegislash's ability to check Xerneas, and so it is best to avoided them. Try pursuit trapping the lLati twins Latios, (AC) Latias, Mega Gengar, (AC) and Deoxys-A, but be careful if the opponent has both a Xerneas and one or of the aforementioned threats.
Team Options
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Clerics such as Xerneas and Clefable can help cure status effects for Aegislash, while Aegislash can Pursuit trap threats such as like Mega Gengar for them. Clefable can also provide Wish support, while both Xerneas and Clefable can help check Yveltal for Aegislash. A solid Primal Groudon check is a must, as all Aegislash can do to punish it is to Toxic Primal Groudon on the switch in. Lugia and Ground Arceus can performboth take on this role, (RC) while Arceus-Ground can also do this, andalso being able to Defog away entry hazards. Other options for entry hazard removal include Giratina-O and Tentacruel, while Mega Diancie's Magic Bounce ability can help prevent entry hazards going up altogether. Last but not least, remember that Aegislash is a utility Pokemon that should fit the needs of your team and so should not be built around.
Other Options
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Aegislash is very specialized, and so it does not have many alternative options that are viable .. (removed space before period) Sacred Sword can be used to lure out in Heatran and Ferrothorn, (RC) and 2HKO them. Head Smash can be used to lure and 1HKO Ho-Oh, but has large recoil damage. Rock Slide is an alternative to Head Smash that comes without the recoil, but fails to OHKO Ho-Oh without rStealth Rocks up damage. A RestTalk set can be used,; however, (AC) the recovery is unreliable, and Aegislash sorely misses tToxic. Shadow Ball hits Mewtwo and Primal Groudon for decent damage. A Choice Specs set with Shadow Ball / Flash Cannon / Head Smash / Gyro Ball can be used for the surprise factor, as well as it's reasonable damage output.
Checks & Counters
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**Fire-types**: Heatran is at the top of the list, as it only fears the rare Sacred Sword, but can still can still outspeed and force out Aegislash. Primal Groudon hates Toxic, but takes Gyro GBalls very well, forces Aegislash out, and can set up Stealth Rock or Rock Polish and proceed to sweep. Ho-Oh is very similar to Primal Groudon, but has Regenerator and Roost to heal off Toxic damage, and cans well as being able to (don't make this change) set up a Substitute as it forces Aegislash out. However, it needs to be wary of Rock Slide or Head Smash. (added period)
**Poison-types**: Pokemon Poison-types such as Poison Arceus and Tentacruel can burn Aegislash you with Will-O-Wisp and Scald respectively. As these pPokemon are immune to tToxic, they can switch in and out without fearing any of Aegislash's moves. Poison Arceus can also burn throughAegislash while not being affected by King's Shield, due to Will-O-Wisp being a status move.
**Gliscor**: Gliscor doesn't mind Toxic due to it's ability Poison Heal, (RC) and has aits STAB Earthquake to force Aegislash out. Once Aegislash is forced out, Gliscor can use U-turn to gain momentum, or set up Stealth Rock. Gliscor has to be careful of U-turning, however, (AC) as it can receive an Attack drop from Kings's Shield.
**Dark-types**: Most Dark-types fear Toxic,; however, Dark Arceus can Refresh it off, (RC) and set up Calm Minds as it forces out Aegislash with the threat of a super effective (remove random empty line) Judgement. Yveltal doesn't like Toxic either, but has Oblivion Wing to recover HP Health Points, and can Taunt Aegislash to prevent it using King's Shield again, (keep comma) or fire off a super effective Dark Pulse. Darkrai can take a Toxic if need be, but it's high Speed means that it won't appreciate coming in on a gGyro bBall or a sSacred sSword. It does force Aegislash out, (AC) however, and can set up a Nasty Plot or a Substitute on the switch.
**Steel-types**: Ferrothorn is immune to Toxic, (RC) and only fears the rare Sacred Sword. It can set up entry hazards or sap away Aegislash's health with Leech Seed. Dialga also only fears nothing but Sacred Sword, (RC) and can force Aegislash out with the threat of a Fire Blast, anthen proceed theno set up Stealth Rock on the switch.
**Giratina-O**: Giratina-O doesn't like coming in on Toxic or Shadow bBall, but can hit Aegislash with aits super effective STAB Shadow Force, which can't be blocked by King's Shield.