In launch versions of Nickelodeon All-Star Brawl, Garfield's stage Sweet Dreams was discovered before his official announcement in an unfinished form which takes place at day time, unlike the final version which takes place at night. Additionally, a thumbnail was discovered for an extremely early version of the stage that takes place at sunset and has an opaque lasagna tray. When Sweet Dreams returned to Nickelodeon All-Star Brawl 2, under the name Food Dream, the daytime setting for the stage would be restored.

During the prerelease of Nickelodeon All-Star Brawl 2, a set of placeholder pages were found on the game's website relating to different characters. Most notable of these pages was one for Helga, a character who was in the first Nickelodeon All-Star Brawl and hadn't been seen in All-Star Brawl 2 marketing materials or leaks at that point - this led a lot of fans to believe that Helga would be returning. Ultimately, she would only be a background cameo on the Aquarium stage.

The 2023 game Nickelodeon All-Star Brawl 2 was the first Nickelodeon product where Korra from The Legend of Korra isn't voiced as an adult by Janet Varney, instead being voiced by Jacqueline Grace Lopez, while Nickelodeon Kart Racers 3: Slime Speedway was the last time Varney portrayed the character in 2022. The reason for this is that Varney announced that year that she was stepping down from the role, because she wanted Korra to be voiced by a person of color, much as Korra herself is, following the announcement of a new Avatar: The Last Airbender movie starring Korra to be released in 2025.

Many Nickelodeon fans 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 Fairly OddParents protagonist Timmy Turner 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, holding the international licensing rights and copyright for the first 5 seasons of the show outside of the US, having used this to syndicate the cartoon on the rivaling Disney Channel.

This absence was eventually broken when Timmy Turner appeared in the 2022 Apple Arcade game Nickelodeon Extreme Tennis, and has continued to make sporadic appearances as a playable character since. 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, and this ultimately did not happen for either fighting game. A playtester for Nickelodeon All-Star Brawl 2 alleged that the legal issues with The 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.

Patrick's Super move was originally going to feature a unique squashed model for each character. These were ultimately scrapped for unknown reasons, with Patrick simply slamming down his rock on the opponent without any transformations or unique animations attached.

Prior to Nickelodeon All-Star Brawl 2's announcement, a convincing image "leaked" showing El Tigre in the game, which would be shared by a variety of sources including Jorge R. Gutierrez, the creator of El Tigre: The Adventures of Manny Rivera. It would later be confirmed by a moderator on the official NASB Discord (who has no involvement in the game's development) that the image was actually an art test from another Discord server and not intended to be spread as a leak. Despite this, El Tigre would still appear as playable character in Nickelodeon All-Star Brawl 2, a rather lucky coincidence given the cartoon's obscurity.

Squidward was not intended to have access to double-jump cancelling (a technique from Super Smash Bros. and Super Smash Bros. Melee where floaty characters such as Peach and Ness can attack at the start of a jump to propel themselves downwards, allowing for moves to end quicker) during the design phase. However, the tech was added by accident after a programmer assumed he was supposed to have it. The development team liked it, and chose to keep the ability as a result.