If you take your Pokémon playing serious, then you need this companion app in your life. It's called PKsinew, a companion app/frontend designed to revolutionise your Pokémon experience with a new achievements system and the ability to transfer Pokémon from all 5 games on the GBA.
According to the dev of the program, PKsinew aims to provide an Original Equipment Manufacturer + experience, essentially enhancing the way you play the Game Boy Advance Pokémon games. It runs offline and launches your games and launches your games in an embedded mGBA emulator.

As PKsinew runs offline, you can press a specific combination of buttons to bring it over the game you're running. Think of it like asking Navi for help in Ocarina of Time or Tony Stark talking to Jarvis. Sinew can then look at your saves, determine which game you're playing, and allow you to both transfer Pokémon across games and save Pokémon outside of the game you're playing.
Companion apps like PKsinew make organisation fun. I know I just said that out loud, but stick with me. You can track your Pokémon in a Pokédex at both game level and across all 5 GBA games at once, tracking the critters you've bagged across the entire collection and how your progress is improving eith every save. Talk about having a tidy mind, eh?

Move Pokémon between games and get trade evolutions without the need of a friend with a second GBA, and store Pokémon outside of the game in a mass Pokémon storage system, with 20 boxes, each with 120 slots per box.
There's also a Pokémon rotating event called Altering Cave that never happened in the original games, a system where catching a Zubat engages in a minigame where you can get a random Pokémon from a finite pool of monsters. So, a little bit of game preservation and bringing back ideas that never came to fruition.
You can find out more by visiting the PKsinew page and discover how to download and utilise it!