In an update, more advertisements were added to the game which would appear during replay moments of matches. Despite the game already featuring advertisements, these additional ones received backlash from the community and were disabled from appearing again.

A member of EA's community team posted a statement via reddit:
"Earlier this week, the team turned on ad placements in EA SPORTS UFC 4 that appeared during the “Replay” moments in gameplay. This type of advertising inventory is not new to the UFC franchise, though we have typically reserved displaying ads to specific main menu tiles or Octagon logo placement. It is abundantly clear from your feedback that integrating ads into the Replay and overlay experience is not welcome.

The advertisements have been disabled by the team and we apologize for any disruption to gameplay that players may have experienced. We realize that this should have been communicated with players ahead of time and that’s on us. We want to make sure our players have the best possible experience playing EA SPORTS UFC 4, so ad integration in the Replay and overlay experience will not be reappearing in the future. Thank you for your continued feedback on EA SPORTS UFC 4."

The game's producer and director Shigeru Miyamoto was asked if he had any references, or anything else he relied on when making all of Mario’s various animations. He responded:

"We tried out a lot of different things using motion capture, but ultimately we ended up doing it all by hand. We created a “skeleton” for Mario that was the basis of his movement."

Lugia was initially created as a plot device for, and only meant to be seen in, the Second Pokemon movie, The Power of One (aka Pokémon the Movie 2000). In fact, his designer, Pokemon Anime writer Takeshi Shudo said he was surprised to see Lugia in the games at all. Game Freak seemed to love the creature so much they not only made him canon, but also made him the mascot of Pokémon Silver.

The original arcade release of Punch-Out!! used two screens at once because Nintendo bought too many arcade monitors after Donkey Kong became a success and with its sales declining, they needed to develop an arcade game to help them get rid of the surplus monitors.

The Windows PC version is an exact port of the Xbox version of the game. Because of this, many of the bugs that exists on the Xbox version were carried over to the PC port. One of the bugs that would occur happens whenever a non-CG cutscene would play. All the character’s that appeared in these cutscenes would have their eyes stay fixed in a forward looking position instead of moving around. This bug does not appear in the PlayStation 2 or GameCube versions of the game.

There are three unused levels still present within the game; an Airship Level, an unfinished version of Fahrenheit Frenzy, and a Warp Room that was presented at E3 2001. Out of the three, the Airship level is the most finished.

The E3 Warp Room is an area containing 5 warp pads, all of which have no collision and will not warp the player anywhere. Interestingly, each warp pad has a hologram of their respective levels overlaid on the pads. This feature isn’t used anywhere in the final game.

The Airship level and the E3 Warp Room can be accessed through Action Replay codes on the North American GameCube versions.

In the PC version, there are several unused animations stored in the game’s files. These include animations carried over from Generations for Classic Sonic, a goal post animation from Generations, a “seek” motion for The Egg Pawns, a damage animation for Silver, early boss fight animations for Metal Sonic, and hand motions for The Golems from Capital City.

Jun was planned to be added into the arcade version of the game, but was later cut some time during development. Her data still exists within the game’s code and can be accessed using MAME cheat files. When added back in, she uses Nina’s character model and Jin’s moveset. Her voice and portrait does exist, but there are assets taken from Tekken 2.

Game's landscape designer Masato Nishimura stated on Twitter, that Wacky Workbench was originally called 'Crazy Toy Box'. The reason for this change was unknown.

In international versions, there's a cutscene of removing the bomb from inside of Paz's stomach at the end of the main mission. The Japanese version however adjusts the camera angle so that no blood and gore is shown on screen.

Originally, the Special Stages were going to have Sonic navigate a rotating maze, building upon the framework of Sonic 1's Special Stage. Although similar, Sonic CD's Special Stage was planned to have two rotating layers that the player switched between.

According to BEEP and Marukatsu MegaDrive magazine interviews, with game's planner Hiroaki Chino, the developers thought the Special Stage was very slow, so they decided to redo it to make better use of the Sega CD hardware.

The PlayStation release was originally intended to be just a single CD game, however a last minute oversight with the size of the game's audio caused it to be shipped as a two-disc game. Though it could've been possible to reprogram the audio algorithms so it could all fit into a single 700 MB disc, as development was already behind schedule it was too late to do this, meaning higher manufacturing and shipping costs on an already tight budget.

The game's director, Hideki Kamiya, has attributed the decision and error to his youth and recklessness at that point in his career.

At one point in development, Pinna Park was meant to function as another hub area. This is evidenced by the fact there are four unused "gate" objects found in the stage's files. These include a ring of manta rays, a shell containing a portal to Noki Bay, and a portal that goes to Pianta Village. The stage also has a MarioPositionObj, which controls where Mario ends up after leaving a course. The only other stage in the game that has gates and MarioPosition objects is Delfino Plaza.

There is anti-piracy protection within the Dreamcast version of the game. If the console detects that the game is running from a copied disc and not an official GD-ROM, Eggman will be locked in death cycle at the start of his section in Cannon's Core. He'll immediately start falling through the floor, dying and respawning in the same position repeatedly. It's still possible to reach the end of the level, but visual glitches and a fixed improper camera angle will hinder the player's attempts to navigate the level.

The Japanese version of the game contains downloadable maps featuring Japanese swimsuit model Yukie Kawamara that was only accessible via codes that were in specially marked boxes. In these maps, Kawamara's breasts are small bumps in the platforms that the player can roll on. This may have been deemed inappropriate for a kid-friendly game, which is why it hasn't been available in other countries for download since its release.

In June of 2020, the game's creative director, Ashraf Ismail, had to step down during development due to accusations that he'd been having extramarital affairs with younger fans of the series.

Ismail made a statement on Twitter saying "I am stepping down from my beloved project to properly deal with the personal issues in my life, [...] The lives of my family and my own are shattered. I am deeply sorry to everyone hurt in this."

Italian model Fabio Lanzoni appears on the game's cover as the protagonist Kuros. Despite this, Kuros appears throughout the game in a full suit or armor.

The game's cover artwork originally featured the American flag and green gaseous fumes, and on the back the words "WANTED: Deadly Force Authorized", "deadly arsenal" and "terrorists". However, due to the then recent 9/11 terrorist attacks and the anthrax scare, the game had been recalled with these removed and the back text changed to make it more politically correct. This pushed back the game from its original September 25th, 2001 release to early November 2001. Some copies with the original box art had already shipped, making that version a collector's item and dubbed the "9/11 American Flag Cover". It also came in a dual case, despite the game only having a single disc.

In 2020, a Beijing court ruled that the 2018 Chinese fantasy comedy film Warrior Angels had infringed on SNK's copyright as some of the characters in the film resembled designs from The King of Fighters series. The film's character Qiao Fan transforms into a "red clad woman" which heavily resembles Mai Shirainui in her appearance as well as in her movement. SNK China was awarded in damages the equivalent of $111,500 with the film ordered to be pulled from distribution. However, the ruling is being appealed.

Trip Hawkins, president of the 3DO Company, sent an angry email to John Rousseau, president of video game review publication GamePro, which was the first publication to review Portal Runner, after it gave the game a low score of 2 out of 5. Hawkins threatened to pull advertising from GamePro and believed that because their review was the first published it would "set the tone by telling the hardcore what to think." Hawkins also described their review staff as "angry young men that are poorly trained and represent a narrow and anarchistic element of the world's population."