The Afterburner kit[1]? I installed a small number of those for friends back in high school, was good fun. I remember the scariest moment while working on a friend's device was accidentally ripping off one of the buttons' contact pads while trying to solder onto it, and having to carefully scrape away the paint over a nearby trace to solder onto instead. He never knew :)

[1] https://www.gameboy-advance.net/accessories/gba_afterburner_...