Christopher Near, the artist who painted the box art for Nickelodeon All-Star Brawl, posted an image to his Instagram of concept art for the game which predates the game's development and was intended to excite Nickelodeon executives over the concept of a Nicktoons fighting game as opposed to influence the product itself - this poster featured a few characters who would not appear in the final game:

•Jenny Wakeman and Rocko, who would appear in the DLC.
•Jimmy Neutron and Raphael, who would appear in the sequel.
•Casey Jones, Krumm, and Angelica Pickles, who have not appeared in a NASB game.
•Wanda from The Fairly OddParents and Reggie from Rocket Power, two shows that have never been in a NASB game.
•Stimpy as a solo character instead of a team with Ren.

Interestingly, despite predating the game's development, it features 80s designs for Rapheal and Casey Jones despite the eventual developers of the game saying that Nickelodeon wanted the 2010s Turtle designs.