If you could add any one feature to vanilla FireRed...

If you could add any one feature to vanilla FireRed, what would it be and why? With the state of FireRed hacking being ridiculously advanced based on my observation of Skeli's Complete FireRed Upgrade and Dynamic Pokemon Expansion, I truly feel like you can do anything in FireRed with enough knowledge/experience. For me, it'd be a hacked version of the move relearner's code that can teach a Pokemon any move it can learn, whether learnset, TM/HM, move tutor, or egg move.

Thanks

easily no HMS and the physical special split, oh and the, of course, get rid of the national dex limitations, like let me evolve golbat jfc.

No version exclusives. Completed Regional Dex possible.
I think Edfrick already mentioned the other obvious ones.

(hi I just Joined) if I could add one feature it would be where you could evolve any Pokemon in the game without that stupid Question Mark at the Evolution Screen (p.s. I'm hacking fire red and I'm trying to do just that any help would be Appreciated)

Since the other prominent mechanic changes have already been mentioned, I'll say the probably unpopular thing, Contests. I wasted way too much time playing through those in vanilla Emerald. Thought they were super fun.