MON-FS is here to solve a problem nobody has ever had, and enables you to store a colossal 3.5kb of data in the PC of your Pokemon Emerald save. The principle here is nothing revolutionary, but the fact somebody went out of their way to make it is worth talking about in itself. The way MON-FS works is by utilising each Pokemon slot in your PC, with each slot acting as 68 bits of data. To keep things simple, only things you're able to see at catch time are factored in, with two bits representing the four most common species on Route 116, 60 bits being the Pokemon's nickname, one bit for its gender, and five bits for whatever held item it's given. By processing each Pokemon in the 14 available boxes, these bits are interpreted and can be converted back to whatever data you used as an input. Creator Paul Sarda uploaded a YouTube video explaining the process to truly highlight its capabilities:
Beyond just the system of encoding and decoding, a modified version of shiny hunting bot pokebot-gen3 was released to assist in catching the Pokemon you're wanting. If you happen to have a lot of free time and are interested in trying this out for yourself, you can find both the GitHub page and a site created for encoding and decoding below.
MON-FS
GitHub Page