Pokémon LeafGreen
While I got Pokémon FireRed, my brother got Pokémon LeafGreen. The two games are functionally identical with only a few changes between them, those being roughly 20 version exclusive Pokémon. I don't have too many memories with the game outside of playing with my brother, but I finally got to play a little bit of it during my "Professor Oak's Challenge" in my FireRed run.
I mentioned that LeafGreen is identical other than the few exclusive Pokémon and that's entirely true. The games are so alike that you can use the save file from one version on the other with no issues. So all I had to do was retitle my save and with the help of my Analogue Pocket, I was able to just pick up where I left off and catch whatever version exclusive I was missing.
You're also able to use lovely programs like PKHeX to mess around with any mainline Pokémon save. With this, I was not only able to get the other starters, but also the other fossil! There's also a great little device called the GB Operator made by Epilogue. It allows you to not only download your save file off of Game Boy, Game Boy Color, and Game Boy Advance games, but also the ROM file. You can also play your games right on your computer with the built in emulator. With these tools I was also able to restore some events that were lost to time.
Overall my journey through Kanto once again was a lovely little romp and seeing some aspects from LeafGreen, no matter how minor was super cool!