Yeah, I do have way too many game ideas for Aozora's Adventure, four of which (outside the Oriental and Darkness sub-series) don't have any defined villainous groups like the main trilogy of Mario-style platformers (plus Gaiden), the first Aozora 64, and the three Mega Man-style games.
The four games are Aozora RPG, Aozora's Adventure 3D World, Aozora's Adventure 64 2, and Aozora's Adventure RPG 2.
Unlike the 2D Mario and Mega man styled platformers, these four games have not really been high priority for long enough to make me decide on the team of villains Aozora and/or his current allies would face. And unlike the higher-represented antagonists from the aforementioned platformers, these antagonists would have little to no possible representation in spinoffs.
RPG's series of villains is undeveloped- It would have a main villain that's unique to it (with Joker becoming a secondary antagonist) along with several other villains. A few of them would pay very light homage to villains from both Super Mario RPG and Mario & Luigi: Superstar Saga.
3D World's league of villains would all serve Robo-Aozora and would contain eight key members and at least sixteen (maybe seventeen) lesser members.
Aozora's Adventure 64 2 is probably the most thought-of the villain groups, being a loose tribute to the antagonists of Final Fantasy X (the leader having a hairstyle and head/face shape similar to Seymor Guado) and the Organization XIII form Kingdom Hearts. As Aozora travels through the timelines/alternate realities in the game (Near-Desolate World, Future At War, Joker's Nightmare, Kurayami's Nightmare, and a fifth as of yet named alternate timeline led by the Seymor expy, where he One Wing Angels and becomes a multi-phase final boss in the end). There would be a total of twelve members including the Seymor expy, seven of them being found in the two Nightmare timelines, two in the unnamed fifth period, and the last three (including the Expy himself) in the endgame stages.
Aozora's Adventure RPG 2- being the most recent, is at square 0. No idea of what kind of villains would appear have been thought of as of yet.
As of now I don't really plan to get these groups designed yet (except maybe the Aozora 64 2) since as stated elsewhere I can't kick these projects off just yet.