In the launch version of Nickelodeon All-Star Brawl 2, GIR's voice lines were not artificially pitched up as they were in the Invader Zim series, making it sound as if they had got a very poor replacement actor to those not familiar with how GIR's voice was originally made. GIR's voice actor Rosearik Rikki Simons pointed this out on Twitter, and it would be resolved in a latter update. However, the updated GIR voice lines still don't have the digitizer voice filter he had in the original series.

In December 2023, information spread about Warner Bros. Discovery, which owns Cartoon Network among other major animation brands, potentially merging with Paramount Global, which owns CN's long-standing TV animation rival, Nickelodeon among other animation IPs. Although this deal would not come to fruition at the time, Nickelodeon All-Star Brawl game designer Thaddeus Crews commented that he would take the chance to work on a Cartoon Network vs. Nickelodeon fighting game "in a goddamn heartbeat".

Nickelodeon All-Star Brawl 2, like the first game, contains unused calls from the announcer. Interestingly, a good chunk of these voice calls are for characters who could be clones or otherwise have a similar body shape to playable fighters, such as DoodleBob, Dark Danny Phantom, Nermal, Abrasive SpongeBob, Squilliam Fancyson, and La Tigresa. Perhaps most interestingly, Lucy Loud's ghost ancestor, Lucille Loud, is the only The Loud House character with an unused announcer line, despite the show's protagonist Lincoln having been cut from the first NASB and the show being based on a large ensemble cast of sisters. Michelangelo and Leonardo are the only cut veterans from the first game with unused announcer voice clips. None of them are from new shows, with a technical exception in the form of the name "Tak", which most likely refers to the Invader Zim character, as she would fit a clone role being an Irken invader like Zim, but could also potentially be for the titular character from the Tak series, though this is unlikely given that the game series had effectively been abandoned by Nickelodeon following the cancellation of its animated series in 2009.

Strangely, before the unused voice lines were dumped and publically uploaded to the internet, an almost entirely accurate list circulated online with Goku from Dragon Ball listed as an announcer call, likely a meme-based in-joke regardless of if it is real or fake, a name which was not included when the voice calls got datamined proper.

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.

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.

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.

In Nickelodeon All-Star Brawl 2, Azula is voiced by Suzie Young instead of her original voice actress, Grey DeLisle - despite this, DeLisle returned to voice Frida Suárez in the same game.

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.

Reptar's ice-skating attack resembles Bowser's dash animation from Super Smash Bros. Melee and Super Smash Bros. Brawl.

While most other characters in Nickelodeon All-Star Brawl 2 recieved revamped movesets, Jenny's moveset is nigh identical to her moveset from the first NASB aside from inputs that didn't exist in the NASB 1 moveset template. This is due to moveset and gameplay designer Thaddeus Crews considering Jenny's moveset to be one of his favorite kits from the first game.

In the reveal trailer for Nickelodeon All-Star Brawl 2, a set of gameplay footage from the first installment is shown. This is notable for two reasons, one being that the footage shows off multiple characters not featured in the second game, and that one scene shows a beta version of the Wild Waterfall stage with a smaller waterfall and different colors for the Thornberrys' ComVee. This would lead to a theory that the Wild Waterfall footage was taken from NASB 2 and accidentally inserted into the NASB 1 section of the trailer, which if true would confirm that Lincoln Loud and Leonardo were returning.

This theory was quite easily debunked by Lincoln and Leonardo using their models from the first game while everyone else got revised models, and a KO explosion effect featured in the snippet being different from one shown later in the trailer. Nigel Thornberry's character showcase would later show off a new Wild Thornberrys stage in place of Wild Waterfall, which was shortly followed by a leak showing Lincoln as an NPC cameo on the Loud Castle stage.

It has been implied that Garfield's neutral special in Nickelodeon All-Star Brawl 2 (where he transforms into the original, fatter 1970s version of the character) was originally going to feature him smoking a pipe, in reference to an internet meme based on a 1978 Garfield comic, where the last panel of a different Garfield comic is replaced with a panel of Garfield smoking a pipe with the same design. It is unknown if this was removed by the developers' choice, at the request of Nickelodeon, or at the request of the ratings board, but either way it was likely done to make the game more appropriate for its age demographic.

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.

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. 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.

Rocko's model in Nickelodeon All-Star Brawl depicts him with underwear underneath his Hawaiian shirt, something that is not true of his standard character design in Rocko's Modern Life. This change was reverted in Nickelodeon All-Star Brawl 2 to match his original design.

In Nickelodeon All-Star Brawl 2, Korra has three neutral specials selected based on the context of their use: a water projectile in the air, a non-offense based slippery puddle on ground, and a torrent of damaging water that goes up and down when used with Slime, regardless of location. This move was originally going to function like it contained three extra special moves in the place of one, where you could do another direction input after starting the move to choose a form (not unlike like Gerald's down special move in the final game). When the move was reworked due to its complexity, it was decided to "shuffle around the pieces" into something more easily understood to avoid wasting finished animations and props and having to make new animations close to the deadline.

In Garfield's alternate costume texture, there is a portion devoted to Garfello, Garfield's Ninja Turtle alter ego from the Garfield Meets the Teenage Mutant Ninja Turtles short comic published in the 1992 Teenage Mutant Ninja Turtles Magazine.

There is an unused model of the Statue of David by Michelangelo in Squidward's prop set. This was likely intended for his air down strong, where he slams down with a block of marble, referencing the SpongeBob episode "Artist Unknown", where SpongeBob makes the same statue by accident. The model has a clam on its groin as censorship, just like in the original episode, but does not have the nose Squidward places on it.

One of Garfield's voice lines in Nickelodeon All-Star Brawl 2 is "I'm sorry, Jon", a reference to an internet meme known as "Gorefield", where Garfield becomes an eldritch monster, and usually utters some variation of the line after or during his rampage.