Every character in Nickelodeon All-Star Brawl has an internal codename used instead of their name. These are:

• Orb - Garfield (Garfield is fat)
• Moon - Leonardo (Unknown, but possibly a reference to the opening shot of the '87 TMNT cartoon's theme song being the moon)
• Pizza - Michelangelo (The Ninja Turtles are known to love pizza, with Michelangelo being the biggest fan of the food among his brothers)
• Cheese - Shredder (Shredder's character design was based on a cheese grater)
• Reporter - April (April is a news reporter)
• Mascot - Reptar (Reptar is a fictional character within the Rugrats universe who appears on a variety of products, particularly toys and food)
• Duo - Ren & Stimpy (Ren & Stimpy are two characters who fight as one unit)
• Hero - Powdered Toast Man (Powdered Toast Man is a parody of superheroes)
• Squirrel - Rocko (A running gag in Rocko's Modern Life involves Rocko being mistaken for other animals, such as kangaroos, beavers, and squirrels, instead of a wallaby)
• Snake - Oblina (Oblina has a thin, somewhat curved shape akin to a snake)
• Rival - Helga (Helga has a love-hate relationship with series protagonist Arnold)
• Narrator - Nigel (Nigel hosts his own nature show-within-a-show called Nigel Thornberry's Animal World)
• Chimera - CatDog (CatDog is two animals with a single body)
• Apple - SpongeBob (SpongeBob lives in a pineapple)
• Star - Patrick (Patrick is a starfish)
• Diver - Sandy Cheeks (Sandy is a land mammal who lives underwater)
• Alien - Zim (Zim is an alien invader)
• Pie - Hugh (Hugh loves pie, and his home stage is a giant pie)
• Neo - Jenny (Jenny is a futuristic robot, and quite young, being a teenager mentally and having been built 3 years ago in the show)
• Plasma - Danny Phantom (Danny's main method of attack is shooting ghost plasma rays.)
• Kite - Aang (Aang travels using a glider, which he uses as an attack in NASB)
• Clay - Toph (Toph forms clay structures out of ground)
• Athlete - Korra (Korra partakes in a sport known as Pro-Bending)
• Rascal - Lincoln Loud (Lincoln is a mischievous child)
• Goth - Lucy Loud (Lucy is a goth)

The inclusion of Hugh Neutron in the game as DLC, particularly instead of his son and series main protagonist Jimmy Neutron, was a response to an ironic internet campaign to get the character in the game known as "Hugh Nation", led by Hugh voice actor Mark DeCarlo and YouTubers The Superverse and Uncle Al, following Hugh trending on Twitter due to memes related to the game's reveal. When Hugh performs his strafe taunt in the game, he can say the voice lines "Hello internet!", "Thank you internet!" and "Hugh Nation!", referencing this push. The showcase for Hugh's moveset, which was aired at EVO 2022, mentions Hugh being included as a "thank you" to the devoted Nickelodeon All-Star Brawl community.

Every single fighter intended for the base game of Nickelodeon All-Star Brawl, but not included in the reveal trailer, was leaked at some point:

• April O'Neil, Ren & Stimpy, CatDog, Aang, Korra were revealed on a silhouetted box art provided to retailers and revealed on announcement day. April's silhouette was vague enough that some people mistook her other characters, such as Carly from iCarly and the live action version of Dora the Explorer from the film Dora & the Lost City of Gold, but most fans deduced that is was April ahead of the reveal.
• Ren & Stimpy's inclusion was further proven by the discovery of an ESRB rating for the game, mentioning moves known as "Log Toss" (referencing a fictional toy from their show) and "First Fart" (referencing an episode of their show).
• A model lineup featuring Garfield was discovered from an unknown source before launch, it was confirmed to be real following the official reveal of Ren & Stimpy, whose models lined up with those featured in the leak.
• Toph was leaked by a rogue developer along with the stage line-up and scribbled out images of Garfield and Shredder. Garfield was not identified, but some players did manage to identify Shredder.
• Garfield and Shredder, who were intended for base game but had to be delayed as free DLC, were found inside the game's code through datamining immediately after launch.

Hugh Neutron has a secret command input move based on Chun Li's Hoyokusen from Street Fighter III: 3rd Strike, which can be activated by doing a 360 input then pressing taunt.

In the release version of Nickelodeon All-Star Brawl, the stage Royal Woods Cemetery from The Loud House contained a hazard where tombstones would pop out of the ground, sending any character beneath them flying and remaining as a wall for a short while afterwards. In version 1.5.0, the update that added Rocko as a playable character, this hazard was removed from the game completely, making the stage into a flat floor, similar to Final Destination from the Super Smash Bros. series. The reasoning for this change is because the stage that was intended to serve as a Final Destination parallel, Harmonic Convergence from The Legend of Korra, was considered too long for use in competitive play, and was removed from this distinction in the same update.

At one point in the game's development, SpongeBob's strong dash attack was intended to involve him running with scissors. This was vetoed by Nickelodeon, with community manager Thaddeus Crews suggesting that Nickelodeon may not have wanted a character many children view as a role model partaking in an easily-imitable dangerous activity. The scissors exist in the game files, attached to SpongeBob's model, but in an untextured form with no bones for snipping.

In the final game, SpongeBob's strong dash attack was a slip and fall based on a single frame from the episode "Krabs à la Mode" that became a meme.

An early title screen in the game data suggests the game's original title was "Nickelodeon All-Star Brawl Universe". For unknown reasons, the "Universe" part was dropped.

Previews for new fighters being added to the game showed that one of Jenny's intended pre-battle quotes was "You wouldn't like my brain! It's all circuity and metallic!" While this line was taken from an episode of My Life as a Teenage Robot, it was removed from the final game due to it being associated with a pornographic parody of that episode by Internet animator Zone, which edited the line to replace "brain" with "body."

Thaddeus Crews, a member of the development team and community manager, initially expressed disgust in a now-deleted tweet (the tweet he replied to also having been deleted) that the line was in the game and announced its immediate removal. He later explained that the line was likely added due to a lack of awareness about the parody, the end result of the team being "spread out and not on the same page", while adding that "Most likely someone on the team did know what they were doing by adding it", despite Crews himself being previously aware of and publicly associating the original line with the porn parody prior to its removal from the game.