Hey Alexwolf, pretty cool team you've got here. You're using a tried and true playstyle while also taking advantage of some underrated Pokemon and sets. This is a really solid team, so I won't be suggesting any mon changes, only a few set changes.
So like others have said, Volcarona is a bit of an issue for this team, resisting both of your priority moves, and max speed versions can even set up on Deoxys-D. Kingdra is probably your best response, but if at full health it can keep Quiver Dancing and restore the health it lost with either Roost or Giga Drain. I don't think the solution is a Choice Scarf user, though (especially on Gengar since that sort of defeats the point of Weavile). A hyper offensive team like this needs all the momentum it can get, and I wouldn't want to sacrifice that by putting in a Scarf user. I think the solution is simply changing Deoxys-D's moveset in order to limit Volc's setup opportunities. The change I would recommend is Thunder Wave over Skill Swap. The main use of Skill Swap is to get past Xatu and Espeon, but you already have Weavile taking care of that. As you said, it is cool against Sableye and Gliscor, but Mental Herb already turns them into set up fodder, so I don't see it as particularly necessary. Thunder Wave, on the other hand, is great for preventing set up sweepers from destroying your team while you try to get hazards up with Deoxys. Volcarona in particular is the biggest one you'd want to hit with it, but basically any fast mon can get ruined by it. It fails to get dangerous set up sweepers like Landorus and Thundurus-T, but you already have Weavile covering those. I can also see that your using Ice Beam on Kingdra. The main reason to use this is for Celebi, but you already have Weavile Pursuit trapping that (It can't even get away with BP!), so I'd suggest Draco Meteor or Surf over Ice Beam on Kingdra. Draco Meteor can be nice when you just need a little extra power to get past a wall, while Surf is cool when you don't need HP's extra power, and don't want to risk a miss. Finally, you might want to consider taking Stealth Rock off Deoxys'D and giving it to Garchomp over Dragon Tail. This could be nice if the opponent has Scizor and you would want to get SR up asap, or just getting an extra layer of hazards in general. I understand the benefit of Dragon Tail, but the extra layer of hazards could potentially be more useful over the course of a game. Since you would now have a free slot on Deoxys-D, Night Shade could go in Stealth Rock's place. This would make sure substitute users can't set up on Deoxys, potentially saving you from sacking a mon.
That's all the changes I could think of, hopefully they'll help you out. Good luck with the team!
Edit: Oh, one thing I forgot to mention about using Stealth Rock on Garchomp is that Ground / Fire coverage is really nice to have on a hazard setter because it lets you cover Tentacruel and Forretress at the same time, which can be annoying, even if you do have Gengar. (Volt Switch + Pursuit for Forry and rain Tenta in general are both annoying for Deoxys-D hyper offense in general.)
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