Faith Connors from Mirror's Edge and Natasha Volkova from Command & Conquer: Red Alert 3 were planned to appear in the game as guest characters, but were both scrapped for unknown reasons. Despite this, Faith makes a cameo as a picture on the wall of Gal Force 4's base, and Natasha has leftover files in the game, suggesting that she was cut late in development. Additionally, artwork exists of an old man character who would have appeared in the game as a member of Crescent Moon, but was also scrapped.
As a sort of call-back to Super Paper Mario, the opening scene of The Thousand-Year Door remake features portraits of Mario's partners from Paper Mario. At the end of the game, Spoiler:a new second portrait of the partners from The Thousand-Year Door can be seen alongside it, lining up with the beginning of Super Paper Mario.
The E3 2007 build of the Xbox 360 release revealed that the home console versions were originally meant to have cutscenes fully animated in 3D. A workprint containing these cutscenes shows a mix of finished and unfinished 3D renders and storyboards with placeholder voice acting, with the final game having cutscenes primarily animated in the same 2D digital animation as the show. The Nintendo DS version of the game is the only version that exclusively uses 3D cutscenes.
This build also reveals that the identity of the "sleazy video game producer" featured in Level 5: Mob Rules is Larry Probst, the former CEO of Electronic Arts from 1991-2007 whose name was censored from the script in the final game.
The "Sausage" and "Legendary Sausage" weapons in Holocure: Save the Fans! are based on the mobile games Sausage Legend and Sausage Legend 2, which are known for being played on livestreams by Hololive talent Oozora Subaru and her viewers. According to developer Kay Yu, he was granted permission by the Sausage Legend developers to reference the game via these weapons and its collaborations. In 2023, the references culminated in Hololive working with the Sausage Legend developers to release special skins for Sausage Legend 2 based on Subaru and fellow member Hakui Koyori.
In the bonus level, "Chips and Dips", developer photos with humorous text can be found across the stage. A photo of producer Jeffrey Zwelling was found during gameplay by accident, and to date, the criteria to activate the picture is uncertain.
One room that Madotsuki can encounter in the FC House's basement is a blue, castle-like area populated by several goblin-like creatures. The design of these characters appears to reference the Famicom version of Bokosuka Wars, which features a similar monster on the "you win" and "you lose" screens.
The Poodle Plush collectible item is based on Percy Poodle, the titular antagonist of the Five Nights at Freddy's fangame Playtime with Percy. Rambley alludes to this when presenting the plush to him at the Information Kiosk, noting how it's a "non-Indigo-brand toy", and claiming that it would "make playtime special for a child with poor taste".
The Lumberjack Lab Assistant enemy from Crash Bandicoot 2: Cortex Strikes Back is usually portrayed wearing a red hat and shirt with blue overalls. This design is used for his NPC role in the Dragon Mines stage of Crash Team Racing Nitro-Fueled, but as a skin for the playable version of the Lab Assistant in that game, his colors are inverted, possibly to downplay potential similarities to Mario.
In the April 1998 issue of Electronic Gaming Monthly's spin-off magazine EGM2, the issue's Trick of the Month was an alleged method to unlock Akuma from the Street Fighter series as a secret playable character in Resident Evil 2. In order to unlock him, the magazine instructed players to play through both story scenarios six times each using only the Knife and the H&K VP70 gun on hand at the start of the game, and achieve an A ranking in all scenarios. Once these specific conditions are met, the player would receive some kind of clue that would lead them to the security computer in the Laboratory on Level B5F. At this point in either scenario, players would type "AKUMA" instead of "GUEST" into the computer, and after entering it would be sent to the Save screen and given the option to make a new save file with Akuma's name. After starting this new file, the game would start with Akuma breaking out of a cryogenic tank in an unused area where Tyrants were originally planned to escape from, and make his way through the game without the use of keys, with his main attack being a red Gohadoken used just like a gun by holding the Action button and firing.
In reality, after going through these difficult unlock conditions, entering AKUMA into the computer will not unlock anything, because the trick was an elaborate April Fools' prank (with the exception of the unused Tyrant area, that was real). This prank was the work of EGM2 editor and art director Mike Vallas, who took assets from Street Fighter EX and heavily modified and photoshopped them into Resident Evil 2 gameplay screenshots. It was one of two proposed April Fools' pranks that were in consideration to appear in the main EGM magazine that month, being beaten out by a prank trick for GoldenEye 007 where you could play as previous James Bond actors. Unlike Akuma, they actually were planned to appear in that game, but can only be accessed with GameShark codes.
The Art of Fighting ending, which was a continuation from the ending from The King of Fighters XIV, features Khushnood from Garou: Mark of the Wolves. However, his name changed to Marco in this ending, which was his original name in the Japanese version of Garou: Mark of the Wolves. This was likely due to The King of Fighters XIV's director, Yasuyuki Oda, and art director, Nobuyuki Kuroki, asking on a livestream with SNK community manager KrispyKaiser if the fans would like his original name in future games. The chat overwhelmingly preferred the name Marco.
BFDIA 5b marks the second time in the Battle for Dream Island series where a copyrighted character is used in a way beyond simply being a recommended character (fan characters that are submitted to the production team by fans of the series to potentially appear in official content). Specifically, the 31st level in the game "Encounter" features Lego Brick, who first appeared as a recommended character in the Battle for Dream Island episode "Vomitaco" and is a reference to the LEGO toy brand. The first instance was in the episode "Reveal Novum", where Dora (a stick figure based on the titular character from the animated series "Dora the Explorer" who also first appeared in the episode "Vomitaco") was one of the recommended characters who had a chance to join the competition, but failed due to only having nine votes: she would, however, compete in the show's second season "Battle for Dream Island Again". Additionally, a copyrighted character appearing in a major role would not happen again until years after BFDIA 5b's release, with the release of the spinoff series "BFDI Mini Replicas". In that series, one of the contestants is Ender Rocky, a variant of the main series contestant Rocky who first appeared as a recommended character in the season one finale "Return of the Hang Glider" and is based on the Endermen from Minecraft.
Nicktoons MLB's loading screens include cameos from a variety of Nicktoons characters, including those from cartoons not featured on the playable roster. One of these characters is George Liquor from The Ren & Stimpy Show, a character that series creator John Kricfalusi retained the rights to after being fired from the series, and would use in a variety of cartoons up until his blacklisting from the animation industry in 2019. Since Kricfalusi is not credited in the game's copyright screen (though he is still listed in the special thanks credits alongside all other show creators), it seems that Liquor was included by mistake.
The character Minoru Minorikawa was introduced in 2004 with the release of 3-Nen B-Gumi Kinpachi Sensei: Densetsu no Kyoudan ni Tate!. Debuting in Episode 8, he appears as a reporter for a newspaper, who is looking into the unresolved suicide of a middle school girl named Chiharu Fuyutsuki from 5 years ago (6 by the end of the game). He works alongside the protagonist, who was Chiharu's teacher back then, to uncover the truth behind her suicide.
In 428: Shibuya Scramble, Minorikawa appears once again, but instead of being a minor late-game character, he became one of the leading protagonists of the game. In this game, he is now a freelance journalist who is attempting to help his old friend Toyama (who used to work at the same newspaper company) in gathering enough stories for Toyama's next magazine issue. During the course of 428, Minorikawa begins reminiscing to his investigation of Chiharu's suicide, with the game making a handful of references to the events of Kinpachi Sensei.
However, the English localization for 428 contains a mistranslation within the reference to Kinpachi Sensei, likely because the latter has never been released in the West. The in-game TIPS for Chiharu Fuyutsuki states that "6 years from now", Minorikawa would solve the mystery behind Chiharu's suicide, while the original Japanese makes it clear that it should be "6 years after this incident." The mistranslation would suggest that Kinpachi Sensei is set years after 428, even though this contradicts Minorikawa's journey from working at a newspaper to working freelance.
Donkey Konga 2 features a set of unlockable badges based on not only Donkey Kong Country characters (specifically DK, Diddy Kong, Dixie Kong, and Cranky Kong), but also other Nintendo IPs such as Mario, The Legend of Zelda and Pikmin. The Japanese version of the game also features badges of generic humans.
The international release of Donkey Konga 2 would remove the aforementioned human badges (as well as the Boo badge) and replace them with six extra Donkey Kong Country badges (Funky Kong, Kiddy Kong, Swanky Kong, Wrinkly Kong, Banana Bird, and King K. Rool). Five badges from Star Fox: Assault, another Namco developed game, were also included, featuring the Star Fox team as depicted in that game (Fox, Falco, Krystal, and Slippy) and also strangely enough, Andrew Oikonny; it's possible that this is meant to be a reference to both the Donkey Kong and Star Fox series heavily featuring ape/monkey characters.
Bubsy: Paws on Fire! attempted to raise funds for DLC with a Kickstarter campaign before its launch, which would've added new levels with new themes, mini-games, costumes, and Commander Video from Bit.Trip as a guest character. The Kickstarter was heavily criticized for the confusing structure it had, where the funding goal would merely add extra one-liners and two costumes for Bubsy while the stretch goals were individual parts of a short extra world, known as the "Impossible World". The campaign did not reach its base goal, and Paws on Fire! recieved no DLC.
On the base platform of Irken Armada Invasion, there is a monitor that displays a static image of the Irken insignia. There are files suggesting that this was originally going to be an animation rather than an image, as animation textures exist for a set of clips of the Almighty Tallest taken directly from Invader Zim episodes, and there is an unused how-to-play graphic showing one of said clips on the monitor. It is not known if these clips were planned to be used or if they were placeholders for another animated graphic, and whether they were scrapped for licensing issues with TV footage, distraction issues on a stage made for competitive play, or something else entirely.
In the GameCube and Xbox versions of Harry Potter and the Chamber of Secrets, it was intended for there to be portraits littered throughout Hogwarts of various real world people, specifically developers, their families, and some people the developers forgot about years after the fact (but believed they were involved in some kind of contest). The portraits of family members in particular were included as a coping mechanism, as they were suffering during development.
"We were doing very long hours, and it wasn’t just us suffering – our families were, too. They were supporting us – often suffering in silence. Marriages were strained, children were missing a parent. It seemed only right to put their pictures into Hogwarts; our odd way of showing our love and gratitude. And possibly to remind us what they looked like."
The development team considered these portraits some of the very few elements of the game they were truly proud of. Eurocom requested the portraits be removed without explaining why, something the developers were "too tired to fight".
As a sort of call-back to Super Paper Mario, the opening scene of The Thousand-Year Door remake features portraits of Mario's partners from Paper Mario. At the end of the game, Spoiler:a new second portrait of the partners from The Thousand-Year Door can be seen alongside it, lining up with the beginning of Super Paper Mario.
In the bonus level, "Chips and Dips", developer photos with humorous text can be found across the stage. A photo of producer Jeffrey Zwelling was found during gameplay by accident, and to date, the criteria to activate the picture is uncertain.
One room that Madotsuki can encounter in the FC House's basement is a blue, castle-like area populated by several goblin-like creatures. The design of these characters appears to reference the Famicom version of Bokosuka Wars, which features a similar monster on the "you win" and "you lose" screens.
In the April 1998 issue of Electronic Gaming Monthly's spin-off magazine EGM2, the issue's Trick of the Month was an alleged method to unlock Akuma from the Street Fighter series as a secret playable character in Resident Evil 2. In order to unlock him, the magazine instructed players to play through both story scenarios six times each using only the Knife and the H&K VP70 gun on hand at the start of the game, and achieve an A ranking in all scenarios. Once these specific conditions are met, the player would receive some kind of clue that would lead them to the security computer in the Laboratory on Level B5F. At this point in either scenario, players would type "AKUMA" instead of "GUEST" into the computer, and after entering it would be sent to the Save screen and given the option to make a new save file with Akuma's name. After starting this new file, the game would start with Akuma breaking out of a cryogenic tank in an unused area where Tyrants were originally planned to escape from, and make his way through the game without the use of keys, with his main attack being a red Gohadoken used just like a gun by holding the Action button and firing.
Nicktoons MLB's loading screens include cameos from a variety of Nicktoons characters, including those from cartoons not featured on the playable roster. One of these characters is George Liquor from The Ren & Stimpy Show, a character that series creator John Kricfalusi retained the rights to after being fired from the series, and would use in a variety of cartoons up until his blacklisting from the animation industry in 2019. Since Kricfalusi is not credited in the game's copyright screen (though he is still listed in the special thanks credits alongside all other show creators), it seems that Liquor was included by mistake.
The character Minoru Minorikawa was introduced in 2004 with the release of 3-Nen B-Gumi Kinpachi Sensei: Densetsu no Kyoudan ni Tate!. Debuting in Episode 8, he appears as a reporter for a newspaper, who is looking into the unresolved suicide of a middle school girl named Chiharu Fuyutsuki from 5 years ago (6 by the end of the game). He works alongside the protagonist, who was Chiharu's teacher back then, to uncover the truth behind her suicide.
Donkey Konga 2 features a set of unlockable badges based on not only Donkey Kong Country characters (specifically DK, Diddy Kong, Dixie Kong, and Cranky Kong), but also other Nintendo IPs such as Mario, The Legend of Zelda and Pikmin. The Japanese version of the game also features badges of generic humans.
On the base platform of Irken Armada Invasion, there is a monitor that displays a static image of the Irken insignia. There are files suggesting that this was originally going to be an animation rather than an image, as animation textures exist for a set of clips of the Almighty Tallest taken directly from Invader Zim episodes, and there is an unused how-to-play graphic showing one of said clips on the monitor. It is not known if these clips were planned to be used or if they were placeholders for another animated graphic, and whether they were scrapped for licensing issues with TV footage, distraction issues on a stage made for competitive play, or something else entirely.
In the GameCube and Xbox versions of Harry Potter and the Chamber of Secrets, it was intended for there to be portraits littered throughout Hogwarts of various real world people, specifically developers, their families, and some people the developers forgot about years after the fact (but believed they were involved in some kind of contest). The portraits of family members in particular were included as a coping mechanism, as they were suffering during development.
