Yay! Doubles! Your team is hyper offensive- which is completely fine! Hyper offense is super fun and works quite well in the Battle Maison.
Changes in Bold~
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Charizard @ Charizardite Y
Ability: Contrary
Timid Nature
EV's: 252 SpA / 12 SpD / 244 Spe
-Protect
-Heat Wave
-Overheat
-Solar Beam
Even if it is just the Battle Maison, Protect is still a must-have. You can get rid of threats to Charizard with Serperoir. The given EV spread given allows you to 1) Survive a Thunderbolt from max investment Rotoms, and 2) Outspeed max speed Hydreigon and Kyurem-Black. Not that you'll be seeing them very often, but better safe than sorry. And last, Overheat acts as a nuke to almost anything.
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Serperior @ Life Orb
Ability: Contrary
Timid Nature
EV's: SpA 252/Spe 252/HP 4
-Synthesis
-Leaf Storm
-Hidder Power [Ice]
-Dragon Pulse
In the Battle Maison, you aren't going to see Heatran really, so HP Ground isn't viable like it usually would be (Typing out loud to myself, because HP Ground is the Meta). You have no Ice coverage, and it would be fairly helpful paired up with Charizard for hitting things for x4 Effectiveness, possibly even at +2 or +4. I don't like the idea of Hyper Beam because it has a chance to miss, and it doesn't hit things for massive damage that you don't already 2HKO. Protect is also a good option here, but you have Synthesis, so you don't necessarily need it. Life Orb let's you hit as hard as possible, and you don't need Leftovers because you aren't running Substitute, and you already have Regen with Synthesis.
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Excadrill @ Life Orb / Shuca Berry
Ability: Sand Rush
Adamant Nature
EV's: Atk 252/ Spe 252/ HP 4
-Rock Slide
-Drill Run
-Swords Dance / Protect
-Iron Head / Protect
This set is great, though you're gonna want to have a better, more immediate Sandstorm if you aren't going to run Protect. If you do run Protect, though, you can have Garchomp set up the Sandstorm that turn to safely get the speed boost. Aside from that, Adamant Excadrill hits way harder, and he doesn't need any more speed because he outspeeds pretty much everything in Sand. Your item can be replaced with a Life Orb or Shuca Berry; you're kind of out of options for an item here, because you already have a Life Orb on Serperior. Double Life Orb can work , it may just be a little awkward having 2 Pokémon that hurt themselves as such. Shuca Berry halves a super-effective Ground type attack. You can run a different type of berry if you choose to do so, if you find a different super effective type to be more common.
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Garchomp @ Rocky Helmet
Ability: Rough Skin
Jolly Nature
EV's: Atk 252/ Spe 252/ HP 4
-Dragon Claw
-Earthquake
-Sandstorm
-Stone Edge / Rock Slide
Wide Lens' accuracy boost isn't very noticeable. It's much safer to run Dragon Claw. Rock Slide might help you more in doubles, Because the flinch chance and spread damage is quite strong. As for your item and ability, run Rough Skin + Rocky Helmet to punish physical attackers. Sand Veil is spotlighting your luck and isn't very great anyway.
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That's it! Since it's just the Maison, you should be fine running this. If you'd like a better sandstorm, you can always run Hippowdon or Tyranitar for easy setup instead of Garchomp. Smogon suggests good sets for both if you are curious about them. :)
