Nickelodeon All-Star Brawl has certain side characters (Helga, Nigel, Hugh, Reptar, Oblina) represent their respective series as playable characters. The main protagonists of these series (Arnold, Eliza, Jimmy, Tommy Pickles, Ickis) are absent from the game in any physical form, with only Tommy and Arnold making brief cameos as photographs in props on the Teeter-Totter Gulch stage, and one of Helga's attack props respectively.

Also of note are Raphael and Donatello, one half of the Teenage Mutant Ninja Turtles who are not playable in the game despite their equal importance to Leonardo and Michelangelo, with Shredder and April taking their place. They do feature as a profile icon, but are absent from the Teenage Mutant Ninja Turtles stages. However, there is an unused texture in the files for the Rooftop Rumble stage that shows all four turtles as a poster, suggesting that they could've appeared in the same capacity as Tommy and Arnold.