Teambuilding Process:
Deo-A is required, and loves redirection. Added Rocks Jirachi for that redirection and to break sashes and put things into range. Sash Gengar beats Kang, which is a huge problem for Deo-A, and is incredibly good in the current meta (so long as you don’t try to Icy Wind a Latios). It also helps the trick room matchup with Taunt. Needed something to beat Thundy, so I added Lum Stone Edge Terrak, with Quick Guard to further support Deo-A. At this point I had no water or fire resists, so added Rotom-W to provide that as well as a ground immunity, and as a pivot with its scarf set. At this point I originally added Hydreigon. Then I realized I had no mega and with some help from
Yoda2798, made a few moveset changes to get less donked by Latios and Heatran, and replaced Hydrei with Mega Zard X for its Aegis and Ferro matchups and its ability to pressure everything (especially other dragons) at +1.
Set Explanations:
Deo-A originally had ExtremeSpeed, but with two forms of speed control, quick guard, a speed booster, and a scarfer taking up the other five spots, I realized I could replace it with knock off to make Latios slightly less scary. EVs are obvious.
Jirachi has rocks for the reasons explained above, and Thunder Wave as its form of speed control to help against Rain. EVs live 2 Kyube Earth Powers, outspeed base 70s, with the rest in Def.
Gengar always picks between Taunt, Shadow Ball, Wisp, Icy Wind, and Sludge Bomb, and I needed Taunt for TR, Wisp to beat Kang, and Icy Wind for speed control. So I just had to choose between Shadow Ball and Sludge Bomb, and I already had Jirachi to hit Fairy types and Mega Zard X to hit Grasses, so I went for Shadow Ball.
Terrakion has Lum to avoid getting para’d by Thundy and Stone Edge to OHKO even bulky variants. Quick Guard was chosen to help Deo-A, since I already had Taunt and didn’t feel like I need Double Kick to beat Bisharp.
Rotom-W has a scarf to deal with faster threats and to trick to troublesome things like Ferro and TR setters. Dual electric moves was chosen over Wisp because I already had Will-O and I didn’t want the only move that left me staying in to have as low accuracy/PP as Hydro Pump.
Char X is the standard set from the analysis - lives a Lando-T EQ factoring spread, outspeeds Deo-A after one DD. Earthquake is an option over Dragon Dance if you know the opp is bringing Heatran, but all members aside from Jirachi have ways of dealing with it and Dragon Claw breaks its sub even without boosts.