You would be better off using Ninja Boy engine instead of running this. I have been saying this for a few years now but Ninja Boy as nothing to envy those other toolbox. In fact while everyone stoppped playing Marshadow-Gx and Mew-Ex box, I still use Ninja Box every time i log in and still have a lot of success and a high win rate on PTCGO. I have shown time and time again that Marshadow-Gx or Mew-Ex where worse toolbox decks. People never seemed to realize why but this is just how it is.
First thing to note is that with a Ninja Boy engine, you can rely on hitting different weaknesses to improve a lot of matchup. At the same time, you are less likely to suffer from one particular weakness yourself which translates into running into less auto-losses. Then, there is also the fact that you have a wider array of pokemon to choose from in order to adapt to the meta since some of them that have abilities or traits can be used as attackers and those things you can't copy (Latias-Ex for exemple). The worse counters to those toolbox decks are decks using Alolan Muk or Garbotoxin to disable your draw abilities (or that new power plant) but at least using Ninja Boy to swap your attacker around, you can at least still attack since you are not relying on a pokemon with an ability like Marshadow-Gx or Mewtwo&Mew-Gx which when abilities get shut down, means you have an auto-loss since you can't attack anymore. Another thing I want to had is that Jolteon-Ex is the main component of every Rainbow Toolbox. Using Thunder Mountain to grant you basic immunity on the first turn is not something you can do if you plan on copying the attack with a Psychic pokemon while i find this being very handy occasionally.
So my two cents on using Mew&Mewtwo-Gx in expanded (centered around rainbow toolbox) would be to implement it as a complement to the Ninja-Box engine by adding only a single copy in the list. It gives you a very decent Psychic attacker that synergies well enough with the deck while not making you rely only on a pokemon relying on it's ability to attack. On the other hand, if you believe like every person on this planet that Ninja Boy is bad without giving it a serious try, I will give you my recommendations on your specific list.
- I would not run 2 copies of Glaceon-Ex since it is not used as often as you would think and it has a bad retreat cost.
- I do not think that running Espeon-Ex without spread damage is worth it. Any reason why you decide to include it?
- Try looking into other useful pokemon to include. Here are some of my favorites that could work out of Ninja Box as well: Machamp-Ex, Comfey, Tauros-Gx. There would surely be a few Stage 1 and 2 to mention but I will let you figure this out.
- One thing you need to remember about using stall as your winning condition is that you need to avoid having enough prizes on your bench for your opponent to win by using Guzma/Lysandre or Escape Rope. You need to think of a way to remove prizes from your bench like Ninja Boy into Unown, Parallel City or the new Giovanni's Exile if you plan on benching many Shaymin-Ex or Tapu-Lele-Gx.
- I run 11-12 energies in my Ninja Box deck and I barely ever run out of them so I do not need special charge at all. If you run Sycamore tho, I can understand that you need to include it but I believe that you should test this out and see if you would not be better off using another supporter instead. Or you could possibly remove 2 Rainbow Energies without too much impact.
- Ninja Boy would be useful only if your main attacker can't attack or if you want to hit for weakness in which case 1 copy would surely be enough. I run more copies in Ninja Box because the deck is focused around. It toggles my attacker and helps recycling Shaymin/Lele while clearing my bench by turning them into Unown (and removing free prizes to enable stall as a win condition) when I have a turn to spare. Still consider 1 copy for the same purpose but since you will need it way less, 1 copy would surely be enough.
- I would consider dropping float stones and relying on Guzma instead. Jolteon-Ex as a free reteat so if you use Guzma you can retreat back into the attacker of your choice after without the need of float stone. Even if you choose to keep them, consider going with a split Lysandre/Guzma at the very least since you have a free retreat pokemon to combo with.
- As others stated, you will need to include at least 1 or even 2 stadiums. I think that the main ones here would be Dimension Valley (not in your current decks actual state since the requirements are 1 color and 2 colorless energies) or Parallel City.
Best of luck,