I'm making a Cobblemon addon which adds a randomly generated league to every world. Eight types are selected randomly for the Gyms and four types for the Elite Four, while the Champion is more tailored (but still semi-randomized). Each type has multiple Gym variants (like Water has a desert variant and an ocean variant (like Pacifidlog)), and each Gym building is further randomized with a random Gym puzzle corresponding to that type. The Gym Leader actually appears in the arena and has multiple lines of dialogue depending on different situations. You need to craft a Badge Case to challenge the Gyms, which shows you your collected badges. Each Gym has eight different teams depending on which order you challenge them in, and the teams are intelligently generated to feel natural. The Elite Four has a 50/50 chance of being gauntlet mode (like Gens 1 - 4) or open mode (like Gens 5+), and has different building variants and levelling algorithms to suit each type. Even the rooms are swapped out depending on the type of each Elite Four member. Every world has a unique League making it fun to challenge each time. I'm also planning on making Gyms spawn as full cities, but that's going to be a lot of work. Still need to create all the Gym variants and puzzles, as well as literally many hundreds of lines of dialogue and NPC skins.