In the special intro between Roger Jr. and Leroy Smith, he finds Roger Jr.'s mother has Leroy's dog Sugar stuck in a headlock. Leroy comes to free Sugar and punches Roger Jr.'s mother in the process. This is a reference to a viral video from 2016 showing an Australian man saving his dog from a kangaroo and punching him in the head in the process.

According to assistant director Juilan Spillane, most of the Silicon Knights staff working on the game were not X-Men fans and lacked knowledge of the franchise. Whenever employees who were more familiar with Marvel and X-Men lore attempted to inform project leads about errors, they were immediately shot down. Spillane specifically recalled being shown an early build of the game with a boss fight against the Juggernaut (a character who is invincible to all forms of physical damage, only being vulnerable to mental attacks) where his health bar depleted to zero. When asked what he thought, Spillane replied: "There's no way Marvel is going to approve this." The complaint was shrugged off and sent to Activision and Marvel for approval; in response, Marvel sent back several copies of "Marvel Encyclopedia Vol 1 X-Men" for the developers to use as a reference. In spite of this, Juggernaut's X-Gene is still available as a selectable suit and power, despite him not being a Mutant in most Marvel media.

As Mileena takes damage during gameplay or performs certain fatalities, her eyes will switch from being Edenian Spoiler:(impersonating Kitana) to having a more feral Tarkatan appearance.

The final scene where Spoiler:Ellie is attempting to reconcile her relationship with Joel after she learns Joel saved her life shortly after the end of Part I was originally supposed to be shown at the start of Part II. Originally, director Neil Druckmann was going to have the scene where Spoiler:Ellie would hug Joel right after their conversation. However, Ellie's actress Ashley Johnson disagreed with this idea saying "I'm not there yet, I can't." Joel's actor Troy Baker was unaware that this scene would be at the end of the game until afterwards, but believed it made for a better sequencing as Spoiler:the scene ending without the hug made their relationship tense and unresolved at the start of the game.

The Game Over screen for the game shows three Mormon men standing next to the gates of Heaven. This is a reference to the season 4 episode "Possibly", where it's established that Mormonism is the one "true" religion in-universe.

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.