Franchise: The Fairly OddParents

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.

Many Nickelodeon fans have noticed a significant omission of characters from the series The Fairly OddParents in Nickelodeon crossovers starting in 2008's SpongeBob SquarePants featuring Nicktoons: Globs of Doom, which was the final installment in the Nicktoons Unite! series where Timmy had previously been part of the main ensemble cast. The reasoning for this is believed to be due to Nelvana, a Canadian distributor of children's content, who holds the international licensing rights and copyright for the first 5 seasons of the show outside of the US, and famously used this to syndicate the cartoon on the rivaling Disney Channel.

Series protagonist Timmy Turner did later appear in the 2022 Apple Arcade game Nickelodeon Extreme Tennis. In response to a Tweet speculating that this could lead to Fairly OddParents content appearing in Nickelodeon All-Star Brawl, the community manager for the latter game Thaddeus Crews posted a "heads-in-the-clouds" emoji. An All-Star Brawl 2 playtester has alleged that the legal issues with Fairly OddParents are so complicated and strung-out that a former Nickelodeon or Nelvana employee was gifted the copyright to Timmy Turner's pink hat design as a farewell gift.