Overview
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Since the release of Omega Ruby and Alpha Sapphire, Sableye has been given this a brand new powerful Mega-Evolution. It has a great ability as non-before Mega Evolution, as well as after its mega; Magic Bounce is extremely useful and Sableye is the only non-offensive user that has of it, which sets it apart from other Pokemon with thise ability. Furthermore, it has a good typing, which leaves it only with only a single weakness to Fairy-type attacks. It also has a good enough supportive movepool that provides reliable recovery among other things. Mega Sableye has great defenses as a Mega, both physically and specially, that allows it to stop several threatening offensive attackers, such as Mega Kangaskhan, which is completely stopped by Mega Sableye completely stops(passive voice -> active voice). However, Sableye does have some downpointssides.—(full stop/period -> emdash)it is extremely slow once Sableye it has Mega-(remove hyphen)Evolved., (full stop/period -> comma) and it also has a mediocre HP stat that lets down undermines its good defenses a bit. Additionally, Sableye has quite low offensive stats, both on the physical and on the special side., and aside from despite its good defenses bulk (changed this for the sake of variety; the phrase "good defenses" was used on the previous line), Sableye is still unable to check several physical attackers, such as offensive Groudon and Mega-(remove hyphen) Salamence.
Utility
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name: Utility
move 1: Foul Play / Knock Off
move 2: Will-O-Wisp
move 3: Recover
move 4: Taunt
ability: Prankster --> Magic Bounce
item: Sablenite / Leftovers
evs: 248 HP / 124 Def / 136 SpD
nature: Impish
Moves
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Foul Play hits physically offensive attackers very well that have a high base Attack stat,such as Deoxys-Attack and Mega-(remove hyphen)Salamence very hard. Knock Off can be used over Foul Play, as it cripples Pokemon that are item-reliableant, as well as it doesing quite a lot of damage against those weak to it, and it also is a generally safe move to use if you're unsure what the opponent is about do. Will-O-Wisp cripples all physical attackers bar those immune to it, leaving their attacks half as powerful. Recover allows Sableye to steadily recover from damage done by opponents. Taunt is a good supporting move that disallows prevents the opponent to from setting up. Protect is another option to use that helps Sableye Mega-(remove hyphen)Evolve safely without needing to take a hit, but cannot KO a weakened Pokemon, unlike Fake Out. Fake Out is an alternative to Protect and can be used too instead, as it helps Sableye Mega-(remove hyphen)Evolve without needing to takeing (changed this bit for the sake of variety) a hit and deals damage, but this it doesn't affect Ghost-types and deals mostly only minimal damage.
Set Details
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The investment in HP helps to patch up Sableye's mediocre bulk by a bit (I assume this bit is referring to Sableye's bulk before Mega Evolving), and the Special Defense investment ensures that Sableye is only 3HKOed by Mega Mewtwo Y's Fire Blast, and can proceed by to beating it with a STAB attack after. The rest of the EVs go into physical Defense to help Sableye beat physically-(add hyphen)based attackers a little bit better. Leftovers can be used over Sablenite to give a Sableye passive recovery very turn as well, and as Sableye it can still profit from continue to utilize (Mega Sableye does benefit from Prankster on the turn it Mega Evolves) Prankster, unlike its Mega-Forme Evolution, which has Magic Bounce as its ability (the analysis has already told us Mega Sableye's ability).
Usage Tips
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Sableye is a good switch-(add hyphen) (for future reference, "switch in" is used as a verb, i.e "to switch in", and "switch-in" refers to a Pokémon that often switches in on another e.g "Anything is a good switch-in to Magikarp)in into a handful physical attackers, such as Mega Mewtwo X, anti-lead Deoxys formes and Normal Arceus (Arceus without a Plate is simply referred to as "Arceus") as it can burn them after and eventually Recover if needed. However, watch out with switching it in;(add space between semi-colon and the word after)between because of its unreliable bulk without Mega-(remove hyphen)Evolution, it is recommended is to that you switch Sableye in after an ally ("ally" refers to a partner on the field in a double battle) teammate has been beaten by a physical attacker. Make sure to use Knock Off whenever you're not sure what the opponent is gonnaing to do, as it is a safe move in general. Using Knock Off against Pokemon that rely a bit on their item, such as Latios and Latias, is also good. Once Sableye has Mega-(remove hyphen)Evolved, it's handy to switch it into on a predicted status attack move, as it will bounce it back and you'll be mostly able to take advantage of the move. Also, don't always Mega-(remove hyphen)Evolve Sableye directly immediately; if there are several physical attackers on the field opposing team ("several physical attackers on the field" would imply that it's not a Singles format) that can be weakened crippled with a burn, make sure to keep Sableye in normal forme from Mega Evolving, as it will be able to pull off a priority Will-O-Wisp against all of them in each case. Use Taunt at best when a defensive Pokemon is on the field, as it'll prevent it from using any status attack (I'd add an extension here such as "reducing its usefulness"; otherwise we're simply told what to use Taunt against and what it does).
Team Options
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Pokemon such as Mega Gengar, Primal Groudon, and specially defensive Dialga are good teammates, as they can that beat up Fairy-types, such as Mega-Gengar, Primal-Groudon and specially defensive Dialga make good partners (reworded for clarity; before it kind of sounded like Mega Gengar, Primal Groudon and Sp. Def Dialga were Fairies). Support from anotherPhysical tanks that beats up the physical attackers that trouble Sableye, such as Giratina, also make excellent partners (changed "tank" to "tanks" to fit with the "excellent partners" bit at the end of the sentence). Partners that appreciate Mega Sableye bouncing back any hazards (this is kind of subjective, but I wouldn't say "any hazards" when the given examples only fear Stealth Rock), such as Lugia and Ho-Oh, make good teammates too. Also, relatively slow Volt Switch or U-turn users, such as Scizor, make good partners as they grant Sableye a safe switch into physical attackers. And Last, but not least, specially defensive Pokemon such as Blissey that can take on the hyper offensive (afaik "hyper offense" is generally only used to describe teams rather than individual Pokémon) Pokemon well that threaten Sableye, such as Blissey, (otherwise sounds like Blissey's an offensive threat, which it certainly isn't) make excellent partners as well.
Other Options
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Toxic is another good supportive moves that hits defensive walls, (AC) (redundant; walls are, by definition, defensive) every turn a bit and eventually wearsing them down, as well as it hitsting Pokemon immune to burns, but Taunt is generally better to assist with wearing these sort of Pokemon down (Taunt can't directly wear anything down). Counter is an option to beat up physically offensive Pokemon with a damaging attack earlier (reworded for clarity) greater ease, but has no uses against special attackers and because of Sableye's low HP stat, (AC) it doesn't do a lot of damage anyway. Trick along with a Choice-(remove hyphen)item can be used to stop defensive Pokemon, but is only useful against one Pokemon throughout the match and is generally done better by other users of them move, such as Gothitelle.
Checks & Counters
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**Fairy-types**: Fairy-types such as Sylveon, Xerneas, (add serial comma; a comma before "and" in a list) and Mega-(remove hyphen)Mawile can beat up Sableye easily with one of their STAB moves, but the latter one (wouldn't "latter" refer to Sableye instead of Mega Mawile if it was used there?) Mega Mawile has to be wary of Will-O-Wisp.
**Fire-types**: Fire-types such as Primal-(remove hyphen)Groudon, Ho-Oh, or and Blaziken, (RC) are immune to Will-O-Wisp and can proceed to beat Sableye with their STAB attacks.
**Strong Special Attackers**: Extremely powerful offensive special attackers, such as Kyurem-White, Darkrai, and Primal-(remove hyphen)Kyogre are, (AC) in most situations, (AC) capable of breaking through Mega Sableye's good bulk defenses (added the "Mega" bit in because Mega Sableye is the one with good defenses, not regular Sableye) with their attacks.