Let's discuss this game.
https://pokemmo.eu/
FAQ:
Q: Isn't this illegal??? Nintendo will shut it down!!!
A: No. The game exists since 2012 and hasn't been taken down. That's because you need the roms for Firered, Emerald, and HG/SS to play it, the game itself doesn't contain any copyrighted material. Everything comes from the roms.
Q: Is it good?
A: Yes.
Q: Does this game have the Physical/Special split introduced in Gen 4?
A: Yes.