Bowser Jr.'s alts have been something I've thought about ever since we started the alt process, and theres no easy answer. Adding 4 palettes for Jr. seems like the easiest option, but then it just seems a little strange that he has 7 other alts and 4 regular colors. That leaves Four new characters as seemingly the only other option, although finding 4 more characters that work with the same rig and are fitting for smash is tough. That being said, I'll share my thoughts on what I view to be the possible candidates.
Just like the koopalings, these guys are recurring mini bosses with koopa anatomy. Boom Boom even debuted in SMB3 alongside the koopalings, although Pom Pom wouldn't debut until Super Mario 3D Land. Seems to be the most obvious choices. Boom Boom's proportions are quite different to Jr., although that didn't stop Iggy. Pom Pom is also not the most important Mario character, but it would be weird to have Boom Boom without her, and we're nearing the bottom of the barrel anyway.
Being essentially the original Jr. Bowser, Baby Bowser seems to make sense at first. However, I'm not in favor of him for a couple reasons. For one, his modern design is almost identical to Jr's. While his original design does look at least noticeably different, this design existed before Bowser Jr. even existed, so its clear that his design has evolved to match Jr's. That reason alone puts me off the idea of him, but the main villain of the Yoshi series being relegated to an alt of a mario character inside a vehicle which he never uses also seems very strange. So while the rig would definitely work, the similarity and status as a Yoshi series character makes him a lot less appealing imo.
Nabbit
Debuting in New Super Mario Bros. U, Nabbit is one of the most recent additions to the recurring mario character lineup. While he doesn't serve bowser, he is in opposition to Mario, as he steals the items from various toad houses multiple times throughout the game resulting in chases. This role puts him at about the same relevance as one of the koopalings within the game itself, although Nabbit's role would continue to evolve. Since Mario was excluded from New Super Luigi Bros. U, Nabbit took his role as the fourth playable character, skyrocketing him to a role which is more than the other Purple Mario character we've added can claim to have had. While this doesn't neccesarily make him more important to the Mario universe than the aforementioned character, it does cement him as an important part of the Mario universe. His relevance is further supported by his smash 4 & Ultimate cameos, playable appearances in Mario Golf: World Tour, Mario Kart Tour, Dr. Mario World, Mario & Sonic at the Rio Olympics 2016, and Bowser Jr.'s Journey, as well as having a Nintendo Switch profile icon ,an
enemy reference in Star Fox Guard, and replacing the
Killer Rabbit in the Mario Minecraft Mashup.
Admittedly I am quite biased in favor of Nabbit as he is one of if not my favorite Mario character, but I think he fits quite well here, and was a popular mod for Bowser Jr. in Smash 4. His role in the New Soup games are similar to that of the koopalings, he's known for stealing items (he steals the clown car to get in to smash), and even has a bandana extremely similar to Jr's for some unexplained reason.
Koopa Kid
I do not like the Koopa Kids. I mentioned Nabbit being probably my Favorite mario character, but Bowser Jr. is in a close second. Koopa Kid is the inferior version of Bowser Jr. He exists solely within the Mario Party series, and hasn't made an appearance since Mario Party 7. He's pretty much retired at this point, with remade versions of old mario party minigames featuring Koopa Kid being replaced by Bowser Jr. instead. He's not even a spirit in Ultimate, so jumping straight to a playable appearance seems unlikely. While his default, green, red, and blue variations being the 4 new alts would make this considerably easier, I think we can do better.
Tatanga
Tatanga is thrown around as an idea for a Bowser Jr. alt quite frequently, although Im not a fan of the idea. Tatanga has never been in a clown car, and would need an entirely new 3D model to be constructed for him, as he's only ever appeared on a gameboy screen and in official art. Tatanga is also extremely obscure, only gaining some relevance after being included as a spirit in Ultimate which I think is a perfectly fine role for him.
Generic Enemy
I guess the proportions would work.... but Piranha Plant more than fills this tiny niche already, and none of them have much business being in a clown car.
Bowser Jr. Alt
While I think Boom Boom, Pom Pom, and Nabbit work pretty well for the first three alts, I have trouble finding a fitting 4th character. given Jr. is already shafted in the alt department compared to every other fighter, I dont think it would be too unreasonable to give him an alt costume instead of a 4th character. Options include a Shadow, Dry, or Cat variants, or my favorite, either his sunshine mask or new soup mask lifted over his mouth. With the Sunshine mask we could even replace all the hammer attacks with paintbrush swipes.
So in Conclusion, I believe Boom Boom, Pom Pom, Nabbit, and a Masked Jr. to be the best path to take. However if a consensus can't be reached I would be fine switching back to 4 recolors since the votes were pretty close anyway.
This was written before Boom Boom, and likely Pom Pom too, were killed
