Oh god I didn't even think of Beast Ring for Rayquaza, that's smart!
Anyway, Rayquaza has to be good post-rotation. Sure you lose great cards for it like Max Elixir, but like Gumball said you still have access to not only Latias PS for the time being, but one set later you get Zeraora-GX which is an instant one or two-of in Rayquaza. I've been thinking about how can I more easily Turbo these energies with these energy recursion effects. If you're already going to use Mysterious Treasure, I was thinking you could also include GRI Oricorio in your deck to search you energies and discard them through other methods (Unfortunatley post rotation means no more Sycamore to discard things we actually want in the discard pile but there are other methods like Ultra Ball and Mysterious Treasure).
He has to be good. The potential to set up multiple attackers all doing crazy amounts of damage sounds super dangerous.
May you explain how Beast ring would be Helpful