I'm pretty content with NASB's roster as it currently stands - The only thing I feel is truly "missing" is a FOP rep, and even then, my requests beyond that are fairly standard: Mr. Krabs, Otis, Dudley if you wanna get crazy with it, etc. However, my most wanted character is someone a bit more unorthadox.
This character (NickBlob, as I'll be calling him) has just under a minute of screentime across his entire history, but he's become an iconic staple of 90s Nickelodeon for many. The main draw for me, though, is his amorphous body. His original bumper
has him morph into a fish and dinosaur, but for NASB, I think it'd be cool if NickBlob could morph into different shapes the Nickelodeon logo has taken over the years, as well as references to other bumpers. One idea I have is one of his neutral airs - He morphs himself into the "burst" variation of the Nickelodeon logo and spin like a buzzsaw. That's only the tip of the iceberg, though - this page has a bunch of Nickelodeon logos that could inspire some moves
Basically, I want NickBlob to be like the Mr. Game & Watch of NASB, except instead of turning into characters from actual Nick shows (although I wouldn't be opposed to a Kirby-style copy ability system), he turns into logos and characters from Nickelodeon bumpers. Will this character ever happen? Probably not. Regardless, he's a character I'd REALLY be excited about.
(Oh, and we could give him a blue alt to reference the Nick Jr. logo, assuming that isn't worked into the moveset somehow.)