Overview
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Escavalier was a Pokemon known by its trollish Pokedex entry and access to a shallow movepool. A few things have changed since then for our cavalry friend. Drill Run was finally put into Escavalier’s arsenal to torture potential switch-ins such as Heatran and Excadrill. Overcoat allows Escavalier to switch into moves such as Sleep Powder and Spore. Knock Off obtaining a buff makes Escavalier an awesome pivot and capable of crippling switch-ins. Finally, the addition of Assault Vest lets Escavalier take special attacks like a champ thanks to its wonderful base 105 Special Defense and plethora of resistances. However, the loss of Ghost- and Dark-type resists do hamper Escavalier’s capability of absorbing special attacks however. Furthermore, not even Assault Vest will always save Escavalier from its quadruple weakness to Fire and its pitiful base 20 Speed. (I know you tried to wrap it up with one sentence combining its flaws and one perk, but it was a bit odd. Assault vest and its speed aren't connected at all, and to me you made it seem like they were. Perhaps end a period after "Fire," which in itself is a valid point, and conclude with a sentence about its worth, plus a true/funny comment about its speed. Just a thought, you can obviously keep it as it is.)
En Garde!
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name: En Garde!
move 1: Iron Head
move 2: Megahorn
move 3: Drill Run
move 4: Knock Off / Pursuit
item: Assault Vest
nature: Adamant
ability: Overcoat
evs: 248 HP / 252 Atk / 8 SpD
Moves
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Escavalier should always run its dual STABs. Iron Head allows Escavalier to tackle threats such as Clefable and Sylveon while Megahorn pierces Tyranitar and Greninja. Drill Run is great for preventing Pokemon such as Heatran and Aegislash from switching into Escavalier freely. The only real choice on this set is between Knock Off and Pursuit, and the choice between the two depends on what your team needs from Escavalier. With Knock Off, Escavalier can be used as a pivot that harasses opponents by forcing the opponent to lose their item (Kind of awkward, "harassing opponents by forcing the opponent" I'd change the wording, or at least add a pronoun). Pursuit gives Escavalier extra utility in trapping potential threats such as Latios, Latias, Alakazam, and Gengar.
Set Details
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This set utilizes Assault Vest as Escavalier’s main item to help it take on Pokemon such as Greninja and Latios. Since Escavalier’s Special Defense stat is much higher than its HP, Escavalier should focus on investing near-maximum HP to sponge attacks from either both spectrums. Maximizing Special Defense yields little difference with Escavalier's bulk. For example, max HP or max Special Defense Escavalier is 3HKOed by Life Orb Gengar’s STAB Shadow Ball. Adamant nature with max Attack EVs help Escavalier maximize its damage output. You can opt for a bulkier spread; however, Escavalier specializes in doing hefty amounts of damage while being utilitarian. If Escavalier is built on a team revolving around Trick Room, a Brave nature with 0 Speed IVs is recommended.
Usage Tips
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Assault Vest Escavalier’s goal is to take on special attackers such as Latios, Latias, Gengar, Greninja, Alakazam, and Deoxys-S while punishing potential switch-ins with its strong dual STABs or Knock Off (Maybe mention Drill Run's damage output on Heatran). One thing to never underestimate is Escavalier’s special bulk - (Okay, I really hate hyphens. This may be just my personal preference, but I'd use a semicolon instead) Clefable with no Special Attack investment fails to OHKO Escavalier (Make sure to mention whether you're talking about Fire Blast or Flamethrower. With Fire Blast, your wording is fine, but with Flamethrower, which is the recommended move, I'd say that it only has a 34% chance to 2HKO Escavalier). Hydro Pump from Life Orb Greninja will fail to 2HKO Escavalier most of the time (most of the time is weird. Specify when [aka when Escavalier starts at 87% or above]) while Escavalier will OHKO Greninja with STAB Megahorn. Specially defensive (Is Defensive supposed to be capitalized?) Mega Venusaur is 2HKOed by STAB Megahorn and Venusaur can only fight back if it has Hidden Power Fire. In sand, you can pressure Bold Mega Venusaur as Megahorn will out damage Synthesis’s recovery.
Team Options
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Escavalier is more of a team player than it is a Pokemon you base a team around. Escavalier can assist teammates such as Keldeo or Mega Charizard Y as Escavalier easily eliminates most of their problematic Pokemon (weirdly phrased. I'd just stick to saying Checks and Counters) with either STAB Megahorn or Pursuit. Rotom-W is a great partner for handling threats such as Talonflame and Heatran while using Will-O-Wisp to help Escavalier take on physical threats. Unfortunately, Escavalier has major issues against Charizard as it can freely switch into any attack Escavalier uses and Mega Evolve immediately. Hippowdon can easily check either Mega Charizard forms thanks to Sand Stream. Alternatively, Goodra and Latias handle Mega Charizard Y while Quagsire can tackle Mega Charizard X.
Other Options
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Due to Escavalier’s poor Speed and shoddy movepool, Swords Dance is better left to other physical sweepers such as Scizor. Choice Band is another item that Escavalier can use as it hits much harder than Assault Vest. As for abilities, Battle Armor is nice, as the chance of an opponent landing a critical hit has had increased this Generation, and makes switching into threats such as Hydro Pump Greninja much easier. Swarm can surprise the opponent when Escavalier is at low health with STAB Megahorn doing massive damage - (same as I said earlier. I'd change it to ", which is enough...) enough to OHKO specially defensive (again, similar comment. Should Specially and Defensive be capitalized?) Mega Venusaur after Stealth Rock.
Checks & Counters
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**Fire-types**: Like many Bug-types, Escavalier is a hot topic for Fire-types as they can easily switch into Escavalier's STAB attacks. Charizard has an added perk of not taking boosted damage from Knock Off while being able to scare Escavalier off with its STAB Fire-type attacks. Heatran is capable of taking almost anything Escavalier throws at it barring Drill Run. If Heatran has Air Balloon it can safely switch into Escavalier at least once. Talonflame and Volcarona have to be weary of switching into Knock Off; however, they can easily scare off Escavalier and either boost their stats or attack the next switch-in.
**Physical Walls**: Skarmory easily shrugs off any attack Escavalier throws at it and can either use STAB Brave Bird to dent Escavalier or force Escavalier to take residual damage from Rocky Helmet. Physically defensive Hippowdon takes 40% max from STAB Megahorn and at least wears down Escavalier with STAB Earthquake or Slack Off recovers any damage Hippowdon takes with Slack Off (now that I think about it, the preceding sentence is pretty bad, as you're forced to say "Hippowdon" instead of "it" after "damage due to confusing pronouns. I'd consider rewording it, as it's currently a bit jumbled". Zapdos shrugs off the majority of Escavalier's attacks and can target Escavalier with Heat Wave. Be careful when using Roost as Zapdos is prone to both Megahorn and Drill Run.