I am a sonic fan. I think I know that.

The best way to get to files like that from any datapack is to download the datapack, right-click the .zip, then click extract all. Then, you can navigate to data/legends_untold/loot_table.

Sorry, I originally forgot to put that in the description of the mod page. It should be on modrinth.

I forgot to put this in the description of the mod, so I might need to fix that

They are pretty rare. But just to make sure, you did download Loot Table Modifier as well, right?

The jade orb is most common in jungle temples. It's not in the creative inventory because datapacks just can't do that yet.

Datapacks aren't advanced enough yet to store that kind of player data. Luckily that makes things easier, all you need to do is take away their advancement for finding rayquaza. The command should be /advancement revoke PLAYERNAME only legends_untold:spawn_rayquaza

No, but you can use Mega Showdown for that.

Since it's a datapack, I can't add items to the creative inventory, so if you need it in creative, you need to use a command. Specific a /function command. They are most common in Tera dens, but they can be very rarely found anywhere maps can be found.

Sorry for the late response, but I don't know that much about servers, so I don't know how much I can help.

There are already models for all 6 regis, so maybe them.