Striking off Ridley and K. Rool, any Nintendo villains you guys want that aren't often talked about here?
I personally want King Boo from Luigi's Mansion in.
I want him in because he'll be difficult to implement properly, which always leads to some creativity.
I sat down and thought about it for a good ~10 mins and came up with things that he could potentially do.
Firstly, for his idle, he'd float in place, a few inches off the ground, and when he "runs" or dashes, he has his hands out in front while shaking his head left and right as if he's trying to scare/haunt something.
His "jump" could possibly be Kirby-esque, though I think we're getting too many of those character types. Perhaps it should be limited to three "jumps" before he covers his eyes and falls to his doom or something.
For his B-specials:
Up-B could probably be similar to Dedede where he flies up into the air and drop back down with a shockwave, like he does in the boss battle for Luigi's Mansion 2.
Down-B could probably be several things. He could have a charge move where he builds up electricity in his crown and let it explode as an AoE. He could also summon a portrait frame in front of him that could trap an opponent in a portrait for a few seconds, allowing him to hit them.
Side-B he could probably throw a spiked ball that has physics so that it would roll down hills and sloping platforms. He could also maybe summon a purple ghost that could fly forward and punch an opponent.
For his normals, he'd probably have a neutral A similar to Kirby's with a bunch of jabs with his stubby arms. His forward A could be a tumbling/rolling attack like he does in the boss battle, and his down A could be a chomp type attack.
For his Final Smash, he could summon a bunch of boos that beeline towards the opponents and possess them. The opponents still have control, but every 1~3 seconds, the player can give them a "command" by pressing direction+A, direction+B, or direction+jump, forcing them to execute those commands.
I haven't really thought up anything else for him in depth, but I felt the need to dump my brain somewhere.