I was bored the other day and looking up stuff about pokemon ruby (the first game i ever played; late 90s ftw ) and i found an entire community called pokecommunity which is all things pokemon all the time. they have a section JUST for mods of gba games and some of the stuff people make are incredible.

My favorite hack of a pokemon game is a mod of ruby called "Pokemon Ruby Destiny", which is a three game series made by destinedjagold

(you need an account to see links)

^Theres a link to the hacks showcase section if you want it

(EDIT: please notify me if this is breaking the rules of some sort and i'll change it immediately)