>>56293610If you want gen 3 but with more mons, I recommend KittyPBoxx's map randomizer. It is FireRed, CrystalDust and Emerald all in one. You need to patch CrystalDust onto an Emerald ROM and have the other 2 vanilla ROMs. You can turn the map randomizer off and switch between regions at will. It is it's own emulator and if you download instead of running it online, I suggest running index.html in Google Chrome. Only downside is because encounter tables are vanilla FireRed and Emerald I do not think you can catch all 386. You should be able find a document on CrystalDust's encounters with a search. Plenty but maybe not all Johto mons available. CrystalDust is Johto only.
You normally start the game in Kanto. If you want to also get a Johto and Hoenn starter you must warp to each game, reset the game and start a new game from both the CrystalDust and Emerald title screens. I think you need to Start menu save in between. This will bring the starters back as they are normally missing from Elm's and Birch's labs. It also restores some missing Rival Silver battles.
If you have the version with the FRLG player sprites you will have vanilla Emerald champion. If you have the Johto CrystalDust player sprites, you will have the Ruby and Sapphire champion instead in Emerald and the post-game fight will be different, (but still a fight that has been in vanilla games.)
I haven't tested this, but I don't see it would not work; vanilla Emerald has an Arbitrary Code Execution. (Check PapaJefe's Youtube for tutorial.) It is a glitch but allows you to get the event legendaries in Emerald. I don't see why it would not work in the KittyPBoxx thing, but maybe the champion change affects too much code. I think the emulator may allow you to either warp to the event islands or add the tickets to your inventory so you can take the Slateport or Lilycove ferry.