Hugh has an unused model of a spear, referencing the popular caribou hunting chant scene from The Adventures of Jimmy Neutron: Boy Genius episode "Jimmy on Ice". While it is fully textured and loaded into the game whenever Hugh is, it is not used.

In the pre-day 1 patch version of Nickelodeon All-Star Brawl, Toph had a different taunt, where she raises her arms in the air. After the patch, this was changed to her waving her hand in front of one of her eyes.

When it was announced that Nickelodeon All-Star Brawl's paid DLC characters were due to be revealed, it was with a tweet reading "Back to the lab again". Some theorized this was a tease for either Jimmy Neutron or Jenny Wakeman, both highly-requested characters with a technology theme. However, this seems to actually be a reference to a livestream by Super Smash Bros. Ultimate YouTuber GimR from two days earlier. GimR advertised the livestream for days prior, promising a new technique that would change the game's competitive scene, only to fail to actually start the stream due to technical issues. During the time he was live, he played a looping intermission animation depicting him as Dexter from the Cartoon Network series Dexter's Laboratory and playing the song "Back to the Lab" by Prince Paul and Wordsworth for over an hour. This mistake would become a meme within the Super Smash Bros. community for a short while afterwards. Ultimately, Jenny, Rocko and Hugh Neutron, the latter two not being related to technology, were revealed, and GimR would separately reveal the promised new technique, the "Slingshot", two days after the failed livestream.

Aang and Korra were first revealed for Nickelodeon All-Star Brawl on the Xbox Podcast with footage from their respective trailers. The CGI portion of Korra's trailer was not played, and following the reveal, Aang's trailer would be posted to YouTube, but not Korra's. This led some to believe that a CGI trailer for Korra was never actually made until May 2022, when a YouTuber named socks dude discovered the trailer on the website for i95Creative, the studio that edited the promotional material for Nickelodeon All-Star Brawl.

Although Nickelodeon interfered signficiantly with the development of Nickelodeon All-Star Brawl, moveset and gameplay designer Thaddeus Crews has stated that he was surprised and grateful for the amount of creative control the game's teams were given:

Two of the first direct-feed pieces of gameplay released for Nickelodeon All-Star Brawl were a 1v1 between Nigel Thornberry and April O'Niel, and a 1v1 between CatDog and Lucy Loud. Both of these battles were wildly one-sided in favor of April and CatDog respectively. In the battle against April, Nigel was controlled by a playtester who had never actually used Nigel before; while in the battle against Lucy, CatDog was controlled by Mattias Hakulinen, who - while not a competitive player - was the best NASB player on its development team at the time. It is not known who was playing as April and Lucy.

One divisive element of Nickelodeon All-Star Brawl is how hard it leans into competitive play, which has been perceived as coming at the detriment of content aimed at casual players such as items and a story mode. According to Ludosity CEO Joel Nyström, Nickelodeon specifically wanted the game to be able to attract a competitive audience, and chose Ludosity as a lead development team due to the positive reception of their first platform fighter, Slap City, from competitive Super Smash Bros. players. 2 years later in 2023, the game's gameplay designer and community manager Thaddeus Crews would respond to a tweet from YouTuber TierZoo complaining about a focus on complicated competitive techniques in non-Smash platform fighters, as well as some replies to the tweet complaining about 1v1-based platform fighter design as a whole, with a clarification on why Ludosity's platform fighters have been marketed so directly at competitive players, as well as why he feels other games in the subgenre are marketed as such:

Ren & Stimpy were made a duo fighter in Nickelodeon All-Star Brawl to allow them to interact with one another, something that wouldn't be possible if they were two separate characters. Ludosity CEO Joel Nyström noted that it also allowed development time to be assigned to one extra fighter.

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".

Out-of-bounds on Omashu are two floating textureless rectangles, while Space Madness has an out-of-bounds cube. These were both possibly used during development.

In a sponsorship segment for Nickelodeon All-Star Brawl produced by comedy group Dude Perfect, a flat, horizontal variant of the game's logo is used on a banner. This is the only known use of this logo during the game's promotion.

Various models and textures of Ittle Dew from Slap City are inside the files of Nickelodeon All-Star Brawl, as she was used as a placeholder during development.

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.

In the final update of Nickelodeon All-Star Brawl, Patrick's command grabs gained a glitch that made them unable to penetrate through shields, negating their primary purpose. When asked about fixing Patrick's grabs after the launch of the game's sequel, gameplay and character designer Thaddeus Crews responded "I would if I could".

In 2023, a set of extremely early Nickelodeon All-Star Brawl screenshots were shared through Discord by a developer, showing an aesthetic closer to Slap City and early versions of SpongeBob, Oblina, Leonardo, The Dump, Jellyfish Fields, and - most notably - Rooftop Rumble, based on Shredder's lair from the 2012 Teenage Mutant Ninja Turtles show instead of the 80s TMNT (despite the 80s turtles having already been decided on this point). Also among the images was Hardcore Chores, Rocko's DLC stage, suggesting that a Rocko's Modern Life character may have been intended for base game.

A Twitter post made on the Nickelodeon All-Star Brawl Twitter upon the release of the Garfield DLC shows that his bib alternate costume was originally supposed to be plain white with stains of lasagna tomato sauce instead of clean with red checkers.

Lincoln Loud's neutral water gun move "The Splasher" had to be reworked during development; the original version of the move stunned opponents and could be cancelled into most actions in the game. This was a flawed move design however, as players could simply cancel the move into a waveland and then perform it again, making an infinite combo. If this move stayed in, Lincoln would have had to be banned from early competitive play, much as Michelangelo would end up being. In the final game, the water gun pushes opponents and cannot be cancelled.

During development of Nickelodeon All-Star Brawl, Patrick's gravity accidentally ended up being set to 420 in certain unspecified circumstances. Thaddeus Crews stated that it was kept that way as a joke.

Nickelodeon All-Star Brawl's movesets are modified through mathematical functions. Due to the monotony of assigning these values, certain modifiers' values are set to be pi solely as a joke. Thaddeus Crews, who added the instances of pi, stated in a Reddit post about the use of the number:

When used on the Wild Waterfall stage, the Suck-O-Matic can suck up the log platforms, altering the layout of the stage.