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Except just about every uses Jolly Chomp and all the Adamant ones are Scarfed.
Adamant is indeed the best nature for it. Jolly loses valuable Attack points. Electivire's moves are diverse, but they don't have great power. Only Earthquake/Cross Chop reach 100 power, and those aren't even STABed.
Electivire @Life Orb/Expert Belt
EVs: 6 HP / 252 Atk / 252 Spd
Lonely/Adamant Nature
-Thunderbolt/Thunderpunch
-Ice Punch
-Cross Chop
-Earthquake/Hidden Power [Grass]
Electivire has a supereffective move against most of the common opponents. Choose Thunderbolt if you want to do more damage to physical walls like Skarmory, Weezing, and Forretress. These guys have tons of Defense EVs but little or no Special Defense, so they'll take more damage from a special attack. If you don't care about that, go with Thunderpunch.
Earthquake hits Electric types that you can easily switch into, but HP Grass is good for Swampert and Rhyperior, who aren't very afraid of its other attacks.
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