I played all of the games growing up, all the way up to Emerald. I always wanted to legitimately complete the Pokedex, so...
-> Pokemon Emerald Recharged - a mod of Emerald with QoL changes, graphic changes, change in spawn rates (most noticeable, Feebas) and triggers for Pokemon that normally can't be achieved
-> Earlier I had played Pokemon Definitive Heart Gold - similar to above, but I caught the first 251 Pokemon and couldn't trade them as it was in a different emulator so I just did it all again...
-> Pokemon FRLG+ - a mod that toggles between Fire Red and Leaf Green and a bunch of QoL changes
Using the Pizza Boy emulator I could trade to myself between these two ROMs on my phone. It was cool having an item that let me "trade evolve" and granted access to the event tickets "without cheating" which would let me get Deoxys and so on. The biggest pain was getting Celebi who didn't have an event in the vanilla game so didn't show up in these mods.
-> I used the pomeg berry glitch for Celebi which was hell, as the glitch had been patched in these modded games so I started a fresh vanilla Emerald game to get it, then use the daycare centre and beat the Elite 4 to trade it over to complete the Pokedex!