It's not so Simple Rayquaza

This is low-key one of my favorite casual movesets to jam in Battle Tree. Simple Rayquaza is a menace! You KO pretty much everything with a STAB Clangorous Soulblaze, getting +10 stat boosts with Simple, enabling your Stored Power and Power Trips to effectively be Base Power 220, with a +2 offensive stat boost, and the bulk to survive anything.

On top of that, you get to Mega-evolve into Mega Rayquaza, giving you a second ability in the form of Delta Stream. You can pretty easily 3-0 many Battle Tree opponents with this just by itself. It's what I refer to as the quintessential "value-town" moveset.

With Flying, Psychic, Dark, and Dragon, there are only 6 Pokemon in the game that resist you ([Mega] Mawile, Pawniard/Bisharp, Klefki, and Magearna). That said, it is important to keep in mind that Clangorous Soulblaze is a one-time use, so I would strongly consider Leppa Berry in your item slot for this reason alone. However, it is important to note that Battle Tree does have an Item Clause, so if you give Leppa Berry (perhaps an S-tier item in console-hackmons) to Rayquaza, that means you can't give Leppa Berry to another mon with 4 CFZ's (Crystal-Free Z-moves), which is DEFINITELY something you'd be interested in doing when your opponent has a team of only 3 Pokemon.

You can replace Leppa Berry with almost any item in the game. Since you're on 4 attacks, Assault Vest kinda slots nicely in here, considering you are still quad-weak to Ice which tends to be special. But Life Orb is also reasonable if you don't have another Life Orber.

It's also reasonable to swap one of your Power moves with a Moldy move, such as Sunsteel Strike, Moongeist Beam or Photon Geyser. You can probably replace Stored Power with Photon Geyser if you are worried about Sturdy (which is all over the place in Battle Tree). You can also consider a moldy CFZ move like Searing Sunraze Smash if you want to go all-in on the Leppa Berry strategy, but just keep in mind that you are going to want to lead with Clangorous Soublaze if you are looking for an easy sweep.

Fairies are what you need to be concerned about, as they will instantly stop your cheeky set-up turn. (It's also another valid reason to run a Steel moldy move.) Outside of Fairies? There's not a whole lot in the Battle Tree database that really stops even base-form Rayquaza. There's only a handful of uncounterable Hackmons on Battle Tree, and Simple Rayquaza is probably one of them.