Hey, since it seems like you're improving and just don't really know what the best options are at times, I may as well drop a small bit of advice on these sets.
I'm guessing the reason for this is its innate Imposter-proofability, right? Makes sense, but I wouldn't really recommend leading with it... this seems more like a cleaner set to be honest that you'd use when the opponent is weak.
First off, I would slash Sing over Hypnosis. Both are valid options, but Sing allows you to get past Substitutes... at the cost of Soundproof blocking it completely. Whichever one you want to run is your call, and in the long run it probably won't make a difference.
Assuming you want to keep its capabilities to set up, I'd run Modest with Shell Smash instead of Tail Glow. Deo-A is already frail as-is anyway, and this allows you to get past certain cheesy scarfers. In addition, this lets your coverage moves OHKO Imposter reliably, which is something I'll get into now...
The last moves are suboptimal, in my honest opinion. Dream Eater is a bad move in general, and Dark Pulse... wouldn't have the best coverage. I'd recommend replacing this with Zap Cannon. Paralysis can be nice against some things instead of putting them to sleep. Plus, the most common Dark types in the tier, Yveltal and Mega-Gyarados, get bopped by it, which is always nice. Psystrike over Psycho Boost would be preferred either way, though. A -2 Deo-A is not a good Deo-A.
If you want to run Modest smash, Modest nature will allow this to OHKO any Imposter that gets sent in on it. I mean, sure, Naive already secures a high roll (252 SpA Deoxys-Attack Zap Cannon vs. 248 HP / 0- SpD Eviolite Impostered Deoxys-Attack: 657-773 (93.4 - 109.9%) -- 62.5% chance to OHKO) but Modest is guaranteed. The only thing you're really missing out on with this speed tier is Timid MMY and some scarfers (Base 90s like PDon which will get banned probably), but Smash, assuming you will pick this option, will allow you to outspeed anyway.
If you want to get rid Tail Glow and Shell Smash entirely for more of a nuking set (which is probably the better option), run Blizzard over Tail Glow to hit bulky Dragons like Giratina and Zygarde-C that would otherwise take on Psychic STAB + Zap Cannon really well. If this were MMY, I'd suggest Inferno, but Deoxys-A relies on its Sash, so Inferno isn't a good option.
I see you're trying out an Imposter-proof MRay set. Unfortunately, Scarf Imposter will decimate it anyways by clicking Draco Meteor and combo'ing that into you clicking X.
morogrim ran a (relatively) Improof contrary MRay that completely decimated me, so I'm going to repost it here and recommend that you try running it instead. (I never got to see the natures or the 4th move so if I get these wrong please correct)
Rayquaza-Mega @ Draco Plate
Ability: Contrary
Shiny: Yes
EVs: 252 HP / 252 Atk / 252 Def / 252 SpA / 252 SpD / 252 Spe
Naive Nature
- V-create
- Judgment
- Leaf Storm
- Sunsteel Strike
Only change I'd make here is either Icicle Crash (deals with Giratina, Zygarde-C), Thousand Arrows (deals with Registeel, Aegislash), or Knock Off (deals with Giratina somewhat, Aegislash) over Double-Edge. Otherwise you get walled by things in parentheses that you don't hit.
This was so close to being perfect and that one change needed is Unburden over Speed Boost. That way you can Imprison on the Imposter before they can, 100% of the time.
Lopunny-Mega isn't really very good in this format, and to be honest I would swap this out with something that can take on threats to the remaining 5 members of your team. Perhaps this could be an Imposter Chansey or some other bulky thing (Poison Heal Giratina, Fur Coat Chansey, Magic Bounce M-Audino, Prankster Registeel, etc. depending on what you seem to be struggling with). If it's the latter, it can serve as a soft check to some members of your team and also as a slow pivot to get other members in safely. I would
highly recommend giving it Defog though no matter what you select if it's the latter. That way Deo-A can get in safely later on into the match and clean assuming Sash isn't broken.
Don't forget EVs and Nature imo. Otherwise good enough, Choice Specs > Life Orb every time though
All in all it was much better than your defensive one... I'd recommend doing a bit more research and thought into "what can check or counter what" before slapping random mons on the team, though. It even seems quite weak to just casual U-turn since 3 mons are weak to it, so... watch out for that.