I think Rayquaza GX can be an incredibly fun deck with a lot of sweet options, and I think the Vikavolt variation of it is absolutely not the right way to play it. Assuming a standard 3/1/3 Vikavolt line with 3-4 Rare Candy...you're talking about 1/6th of the deck commited to ONLY energy acceleration and NOTHING else. You're also relying on a stage 2 while relying on things like Dragon Storm Drampa and the Ultra Beasts makes this a full basic Pokemon deck.
I believe that combining both of the other options, such as throwing in a Latias Prism Star and a few copies of Dragon Storm Drampa, as well as playing the Ultra Beast Strategy is likely the best combination for it.
I actually think Rayquaza GX can be better than Vikabulu because it never relies on a stage 2 and has access to Mysterious Treasure in a format where setting up Pokemon becomes a bigger challenge without Brigette. Mysterious Treasure makes your set up more consistent and makes your Leles more consistent as well.
Here are cards I would highly consider for the deck.
Pokemon
1. Full 4 copies of Rayquaza GX - Normally I think that 3 copies of your main attacker is enough, but you want the full 4 copies to make sure you can maximize on its milling ability.
2. 2-3 copies of Drampa Dragon Storm - this is a good card to play early on. Lay down some Rayquaza GX on bench, hope to mill excess energy, and get 3 attaches in one turn - one from Rayquaza GX ability, one from attach for turn, one from Drampa's attack.
3. Latias Prism Star - A 1 energy attack that could possibly put 6 basic energy onto the field at once - that powers up Rayquaza GX to 180 damage, 210 with choice band in just one turn. This is just a mandatory card for the deck.
4. 2-3 copies of Pheromosa GX - A grass ultra beast with a very powerful GX attack that can OHKO things past 4 prizes taken. The turn 1 attack is very good since it deals 30 damage immediately, but it also adds 30 damage to your Rayquaza GX for having a grass energy on it making it a pseudo-60 damage attack specifically in this archetype.
5. 2-3 copies of Xurkitree GX - Gives you special energy hate to wall anyone using Beast Energy, DCE, Counter Energy, what have you. Rumbling waves is a very good 2 hit KO attack, and the GX attack is situationally useful as well. Having both Pheromosa GX and Xurkitree GX in the team also makes sure that you don't get completely swept by Fairy decks like Gardy GX.
6. 2-3 Tapu Lele GX for supporter searching.
7. 2/2 line of Zoroark GX - You aren't hurting for bench space here. Let's get some draw power going, especially because this deck can play some interesting supporters.
Playing Pheromosa GX and Xurkitree GX weakens Latias Prism Star, but the trade off is the access to Beast Ring which can accelerate energy without ending turn. This gives you access to multiple types of energy acceleration for multiple types of situations. Flexibility is best.
Supporters
**4 Cynthia, 3 Guzma, 1 Steven's Decision, and 1 Lillie are implied. Not all may agree with that, but I think it's a solid base lineup of supporters.
1. Volkner - This guy is the reason why I think the Beast Ring strategy is absolutely a must have for the deck. Volkner for Electric and Beast Ring/Mysterious Treasure, then Beast Ring for 2 more energy or search out your Rayquaza GX/Drampa/Latias. This not only guarantees that Pheromosa GX and Xurkitree GX can attack the same turn Volkner is played, but that's one card for instant 90 damage boost.
2. Mallow - Rayquaza GX mills the top 3 cards of your deck on play. Playing Mallow means that you can guarantee mill 2 energy no matter what so that Rayquaza GX will never miss its ability in the early game. One Mallow guarantees that you'll have 2 energy in the discard pile to guarantee that 2 Rayquaza GXs will hit. I think only one copy of Mallow is needed for just in case your hand doesn't see the energy to discard through Ultra Ball/Mysterious Treasure/Zoroark GX.
Items
Personally, I prefer Choice Band over Wishful Baton. You should be spreading your energy intelligently and making sure that you aren't losing 3+ energy to a KO very often. Also, Field Blower is still a thing. I don't run them anymore because Garbotoxin and Parallel City are gone after rotation, but I know many people are still going to. Choice Band is fundamentally extra energy just in case you need that extra attach for turn to close out the deal, kind of the same reason why Choice Band is run in Gardevoir GX (attach DCE, Secret Spring Fairy, attach Choice Band, that's +120 damage in 1 turn).
One Rescue Stretcher and one Energy Retrieval I believe are mandatory in this deck. Rayquaza GX's mill can lead to excess energy or Pokemon loss, and you need to make sure you can recover cards that were excessively milled. Volkner allows you to guarantee seeing your one of Rescue Stretcher and Energy Retrieval.
I don't think this deck needs more than 2 Beast Ring since it's an alternative strategy rather than a core strategy. One copy just isn't enough to me, though.
Also, here is a skeleton list I threw together just as a starting base.
Pokemon x18
Rayquaza GX x4
Pheromosa GX x2
Xurkitree GX x2
Tapu Lele GX x3
Zoroark GX x2
Zorua x2
Drampa (Dragon Storm) x2
Latias Prism Star x1
Supporter x12
Cynthia x4
Guzma x3
Volkner x2
Steven's Decision x1
Mallow x1
Lillie x1
Item x18
Ultra Ball x4
Mysterious Treasure x4
Choice Band x3
Switch x3
Beast Ring x2
Energy Retrieval x1
Rescue Stretcher x1
Energy x12
Grass Energy x6
Electric Energy x6
Likely needs refinement, but I think it combines the best of all worlds for Rayquaza GX. Energy Acceleration, good set up, alternative attackers & type coverage, and various useful GXs.
