The closet in Butters' room contains references to various previous South Park episodes featuring him:

• Butters' hockey mask from the season 5 episode "Proper Condom Use".
• The Professor Chaos costume, first appearing in the episode of the same name from season 6.
• A device Butters as Professor Chaos created to take the cherries out of chocolate-covered cherries, replacing the insides with expired mayonnaise, from the season 6 episode "The Simpsons Already Did It".
• The Eric Cartman memorial from the season 7 episode "Casa Bonita".
• Butters' sparkly pink, tap dancing vest from the season 8 episode "You Got F'd in the A".
• Butters' polka dot pajamas from the season 10 episode "Hell on Earth 2006".
• Action figures of the Council of Nine (Glinda, Jesus, Wonder Woman, Luke Skywalker, Morpheus, Aslan, Popeye and Zeus) from the season 11 three-part episode "Imaginationland".
• Butters' chain from the season 13 episode "Butters' Bottom Bitch".
• Butters' "Texans Vs. Mexicans" costume and a mural during his stint as "Mantequilla" from the season 15 episode "The Last of the Meheecans".
• Vials of "Butters' Creamy Goo" (his semen) from the season 16 episode "Sarcastaball".

Trey Parker and Matt Stone were given many proposals for a freemium South Park mobile game, most of which were based upon the "rebuild the town" structure of The Simpsons: Tapped Out and Family Guy: The Quest for Stuff. Jordan Thomas, the creative director of South Park: The Stick of Truth, advised Parker and Stone of the ethical issues surrounding this, including the possibility of publishers taking the license and essentially disguising the game as a slot machine. While Parker and Stone weren't against the idea of microtransactions, the pitches were shut down due to publishers and developers being more focused on making a game that was addictive rather than fun, comparing them to gambling and the alcohol industry. Three years before the game's release however, these ideas were spoofed in the season 18 episode "Freemium Isn't Free", prompting some critics to call the game's creation and similar predatory use of microtransactions ironic.

In addition to being Spoiler:a cannibal, it is implied in the game and in unused dialogue that Danny St. John is Spoiler:a pedophile, though it is never outright stated. After escaping the freezer and hiding inside the barn, this dialogue exchange happens between Andy and Danny:


There are also unused voice lines where Danny reminisces about school children taking tours of the dairy farm and makes note of the girls' "springtime dresses". Danny's voice actor, Brian Sommer, recounted in a 2012 interview that it was hinted to him in the recording booth that the character was Spoiler:a child molester before the apocalypse, and further implies this as he explains how he voiced Danny:

An intro conversation shared between Scorpion and the Joker has Scorpion recalling meeting him, and the Joker mockingly responding: "Aww, the back of your head still hurting?" This references a cutscene from Mortal Kombat vs. DC Universe, where the Joker uses an extending boxing glove to punch Scorpion in the back of his head as he walks away.

Despite being the eighth mainline game in the series, in relation to Mortal Kombat's continuity, the game's events are considered a non-canon "What If?" scenario placed in-between the events of Mortal Kombat II and Mortal Kombat 3 and not as a sequel to Mortal Kombat: Armageddon, despite featuring characters from later entries such as Quan Chi. Regardless, the events of the game are referenced in Injustice 2 and Mortal Kombat 11. In the case of the latter game, which establishes a multiverse for the series, it is implied the events of the game took place in another timeline.

Before becoming a crossover, the game was originally planned to be a darker reboot of the series under the title "Mortal Kombat 8", inspired by games of the era like Gears of War and taking advantage of Unreal Engine 3. During the planning process however, Midway managed to acquire the DC Comics license, transforming the game into the crossover. The pitch of the game stimmed from series creator Ed Boon always wanting to do a crossover game with another franchise, naming Street Fighter among potential candidates, and so they could have an opportunity to explain why Mortal Kombat and DC Comics characters were fighting each other in the first place, as opposed to Marvel vs. Capcom which Midway senior producer Hans Lo described as "random". Despite this, the game is still considered the eighth mainline Mortal Kombat game.

Postal 2 was the first game to receive the "Intense Violence" descriptor in a rating from the Electronic Software Ratings Board.

The sounds that Donkey Kong makes in many earlier Mario spin-off games starting with Mario Kart 64 comes from "Chimpanzee Screeches and Vocalizes", a recording created by the stock audio company The Hollywood Edge in 1995.

The sounds used for Yoshi's voice in Super Mario World were created by composer Koji Kondo by playing an orchestral hit keyboard preset and pitching it both higher and lower. This sound would go on to be used as Yoshi's voice in several of his appearances throughout the Mario series, even in some instances after Kazumi Totaka became his voice actor.

Various characters from the WarioWare series make cameos throughout Rhythm Heaven Groove:

• At the start of Sneezy Moon, Ashley has a chance of appearing amongst the swarm of bats, using her design from Game & Wario. This is hinted at by the "Magician in the Night" Info Tidbit.
• During Soccer Dreams 2, Mona has a chance of appearing on the bench behind Sora, wearing her cheerleader outfit from WarioWare: Smooth Moves. Similar to Ashley's cameo, this is hinted at by the "Benchwarmers" Info Tidbit.
• In the Try Again epilogue of Synchro Wings 2, the Alien Bunnies appear piloting the UFO that the Migrating Birds are resting on.
• In the Good epilogue of Pet N Parcel 2, one of the Sasquatch Family members from WarioWare Gold is shown accepting the package from the rabbit.

The Snack World: TreJarers features leftover content from games in the Yo-kai Watch series. Specifically, graphics used in Yo-Kai Watch 3: Sushi can be found in the game files, and the sub-directory "archive_a.fa/data/txt/en/movie/sw1_evop_0001_en.cfg.bin" features the following text from the intro of the Yo-kai Watch 2 games:


It's likely these lines were used for testing the game's text engine.

Ports for the Sega Saturn and PlayStation were announced, but were later cancelled.

In the game's manual, Saliva is erroneously referred to as Billy's dog. Within the context of the show, Saliva is owned by Mandy.

In the PlayStation 2 versions of Barnyard, Nicktoons Unite!, SpongeBob SquarePants: Lights, Camera, Pants!, and Tak: The Great Juju Challenge, if any of the games detect the save data for one of the others on a memory card, they will unlock access to certain bits of bonus content. These include:

• Unlockable trophies based on Timmy Turner, Cosmo and Wanda, Otis, Jimmy Neutron and Tak in SpongeBob SquarePants: Lights, Camera, Pants!
• Unlocking store discounts and the Yellow Hornet Bike in Barnyard
• New character skins in Nicktoons Unite!
• A bonus blessing gem, time bonus pick ups, and the Black Mist Car in Tak: The Great Juju Challenge

Billy and Mandy's alternate Robot costumes, and the addition of Horror's Hand originate from the 2007 made-for-TV movie "Billy & Mandy's Big Boogey Adventure". The game released in September 2006, with the film premiering in March 2007, so the addition of these aspects could serve as early promotion.

The final boss of the game, the Brain-Eating Meteor, originates from the season 1 episode "Little Rock of Horrors". The character's musical sequence from the episode, the Aurelio Voltaire Hernández song "BRAINS!", is also featured as the fight's background music. Despite this, the game does not credit Hernández or the song's other co-writers, Gregor Kitzis, Matthew Goeke, and George Grant. Hernández also goes uncredited in the game's cast list despite his vocals from the original episode being retained in-game.

The lack of credit for "BRAINS!" reflects a longstanding issue with the song since its original commissioning, in which Cartoon Network repeatedly failed to properly attribute it to Hernández, instead crediting it to the show itself when airing the sequence as a music video. According to Hernández, the initial failure to credit him resulted in Cartoon Network revealing that it was under no legal obligation to do so, per the terms of Hernández's contract, before eventually pulling the music video from circulation. Hernández stated that he was aware at the time that he would be signing away the song's rights, but did not know until then that the network reserved the right to opt out of attribution. Despite the dispute, Hernández remained friends with series creator Maxwell Atoms and later contributed another song, "Land of the Dead", to the TV film Billy & Mandy's Big Boogie Adventure.

During the level "The Takagi Building", one of the Yakuza members tells a story of a man named Sano, who took one hundred men, powered by MGH (Mutant Growth Hormone), to attack Daredevil. The encounter was said to have gone poorly for the Yakuza members, who were jailed or hospitalized. This dialogue exchange references volume #2 issue #57 of the comic book "Daredevil", where this event took place.