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.

Nickelodeon All-Star Brawl was originally intended to feature alternate palette swaps for every character on the roster, but this was rejected by Nickelodeon, who only wanted costumes that reference the shows directly. The only known planned recolors are for SpongeBob that were based on other characters from the show: Squidward blue, Patrick pink, and Mr. Krabs red.

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 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.

At one point in the game's development, there was planned to be an item based on the character Buhdeuce the Duck from Breadwinners, a Nicktoon infamous for its over-reliance on loud sounds, 2010s slang, and gross-out humor - the item's purpose would be as a punching bag that would do nothing but scream. This was first revealed on the game's Discord server in a now-deleted post, initially being dismissed as a joke or a quickly-scrapped concept. However, upon the game's release, a placeholder item called the "Sleeper" was discovered in the code that served the exact same purpose that Buhdeuce was said to have had, alongside having the same circular shape as Buhdeuce, seemingly confirming that development work had indeed been done on the item. Come the items update, Buhdeuce was nowhere to be seen. It is unknown why he was scrapped, but it's possible that Nickelodeon may not have wanted content directly mocking one of their cartoons.

Despite MultiVersus being positioned by the gaming press and certain players disappointed with the latter game's lack of content as being a "rival" for or having "killed" Nickelodeon All-Star Brawl, the development teams behind both games are fans of one another's work.

In an interview with competitive Super Smash Bros. player Hungrybox, the developers of Nickelodeon All-Star Brawl claimed that the game would feature cross-play in a future update. Cross-play was eventually finished for the game, but was not able to be released due to Nintendo's strict guidelines on cross-play. On March 3, 2023, the game was released on the Epic Games Store, and cross-play between PC and Switch was accidentally added without announcement, but was removed shortly after, though cross-play between Epic Games and Steam players would continue to exist in the game.

Cross-play would eventually be included in the base game of Nickelodeon All-Star Brawl 2 for all consoles and generations.

All of the competitive stages in Nickelodeon All-Star Brawl are - with one exception - inspired by stages from the Super Smash Bros. series:

•Jellyfish Fields, from SpongeBob SquarePants, is based on Smashville, introduced in Super Smash Bros. Brawl.

•Harmonic Convergence, from The Legend of Korra, and the post-update version of Royal Woods Cemetery, from The Loud House, are based on Final Destination, introduced to the multiplayer stage lineup in Super Smash Bros. Melee.

•Sweet Dreams, from Garfield, is based on the frozen version of Super Smash Bros. Melee's Pokémon Stadium, introduced officially in Super Smash Bros. Ultimate, but popularized by fan projects such as the Super Smash Bros. Brawl mod Project M prior.

•Irken Armada Invasion, from Invader Zim, is based on Battlefield, introduced to the multiplayer stage lineup in Super Smash Bros. Melee.

•Rooftop Rumble and Sewers Slam, both from Teenage Mutant Ninja Turtles, are based on the hazards-off version of Smashville introduced in Super Smash Bros. Ultimate, with Sewers Slam - originally intended as a casual stage but adopted into the competitive stage lineup - containing a goop hazard somewhat resembling the wind from Smash 64's Dream Land.

•Duck, Duck, Pie!, based on The Adventures of Jimmy Neutron: Boy Genius is based on the hazards-off version of Super Smash Bros. for Wii U's Kalos Pokémon League, introduced in Super Smash Bros. Ultimate.

The exception to this pattern is Tremorton Joyride from My Life as a Teenage Robot, which is based loosely on Delfino's Secret from the Super Smash Bros. Brawl mod Project M.

Nickelodeon All-Star Brawl contains multiple unused announcer lines - including multitudes of character names (including characters from Rocko's Modern Life and Jimmy Neutron: Boy Genius, which were not represented in the base version of the game), item announcement calls which (despite the narrator having used voice clips relating to the items) did not end up being used, all of the stage names (notably including alternate names for the Slime Time stage in the form of "Double Dare", "Double Dare Stage", and "Double Dare Extreme") and, perhaps most interestingly, lines relating to a shop feature where the player could buy outfits, characters, moves, and stages. The reveal press release for All-Star Brawl references the ability to "unlock advanced moves", which may be referring to this scrapped feature.

Upon the release of the Hugh Neutron DLC, a glitch was added to the Switch version of the game that made Aang's air ball move an instant KO. This was quickly patched out.

Nickelodeon All-Star Brawl was intended to launch with a deluxe edition that would contain extra alternate costumes, much like the deluxe edition made for Nickelodeon All-Star Brawl 2 - this never came to be due to the alternate costumes not being finished in time for launch, with the game eventually receiving a free update to add one costume per character.

Unusually, Rocko's light up air (where he puts on boxing gloves and deals a flurry of punches) is more powerful than his strong up air (where he forces his opponent to look at a painting of a sad crying clown in an iron lung), with the prior move dealing 19% maximum (14% coming from the last hit alone), while the latter move only deals 13%.

Shortly after Nickelodeon All-Star Brawl's launch, the PC version of the game suffered a mysterious anomaly on its online modes informally known as the "items virus", where unfinished placeholder items would show up on the casual quickplay online mode, and then appear in offline modes with no way of turning them off except for restarting the game, all the while spreading the items to anyone you play with online.

Nickelodeon All-Star Brawl notably has certain side characters (Helga, Nigel, Hugh, Reptar, Oblina) featured without their series' respective protagonists (Arnold, Eliza, Jimmy, Tommy Pickles, Ickis) - what is less known is that these protagonists are completely absent from the game in any physical form, with none of them appearing in stage cameos. Tommy and Arnold do make brief cameos as photographs in props on the Teeter-Totter Gulch stage and one of Helga's attack props respectively however.

Also of note are Raphael and Donatello, a half of the Ninja Turtles who are not playable in the game despite their equal importance to Leonardo and Michelangelo, with Shredder and April in their place. They do feature as a profile icon, but are absent from the Teenage Mutant Ninja Turtles stages.

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.

In Garfield's showcase presentation, the narrator remarks "It's time to kick Odie off the table!" when showing Garfield's light neutral attack. This is a reference to "Garfielf", a surreal fan animation by YouTube animator PilotRedSun. While kicking Odie off the table is a recurring gag in Garfield comics, the specific quote "It's time to kick Odie off the table" originates from the Garfielf video and seems to not be from any official Garfield media.

The layout of the Traffic Jam stage in Nickelodeon All-Star Brawl, consisting of a bus driving along moving asphalt that players can fall onto and either ram into the bus or get conveyed off-screen, while cars appear to the left and right to stand on, is recycled from a stage from Ludosity's first platform fighter Slap City called Public Transit, with the main difference aside from the Hey Arnold! theming being the absence of an equivalent to the Apathetic Frog helicopter.

The background music for the Slap City stage is also called "Traffic Jam" on the game's song selector (though the official Bandcamp release and the internal file names call the song "Noisy City" instead) and a sidescrolling stage reusing assets from Public Transit in Slap's story mode is called "Traffic Jam".

Two of the franchises represented in Nickelodeon All-Star Brawl have had installments aimed exclusively at adults. Both of these franchises have their mature iterations referenced within the game, with Ren & Stimpy's taunt originating from the Ren & Stimpy Adult Party Cartoon episode "Fire Dogs 2", and Leonardo and Michelangelo's alternate costumes originating from the original Mirage Teenage Mutant Ninja Turtles comics.

In sports mode, the Arnold football has an indicator above it to inform players that it must be grabbed and not hit - this graphic, however, is a crude placeholder graphic that appears to have slipped into the final game.

When Garfield was released as a playable fighter in Nickelodeon All-Star Brawl, Twitter user InsaneProtayto posted a viral tweet with a fake screenshot of an IGN news article claiming the cat couldn't be played as on Mondays, referencing one of his most well known catchphrases, "I hate mondays". This hoax ended up becoming so popular that publisher GameMill Entertainment had to post a statement on Twitter confirming that Garfield can in fact be played as on all days of the week.

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)
• Michelangelo - Pizza (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)
• 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)
• Mascot - Reptar (Reptar is a fictional character within the Rugrats universe who appears on a variety of products, particularly toys and food)
• 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)