Famous works of fiction are often told, retold, retooled, inverted, and re-imagined five ways to Sunday. In many of these tales, some characters will overlap, some notable items may be present in several... in fact, when entirely NEW stories are written, authors will give nods to earlier stories, subtly referencing things that were popular, or not, about earlier iterations of a mythos.
Maybe Optimus Prime will have an odd aversion to gorillas or apes in general. Maybe Conner Kent will try on some round sunglasses before taking them off. Maybe Sherlock Holmes will pass by a music shop, and, on a whim, pick up a violin to try and learn to play it.
When self-contained and unique, this is called a Mythology Gag. A single work may even contain several, or many, such gags.
But when a work becomes heavily inundated with, or a work's entire raison d'etre IS to be laden with as many mythology gags and/or characters as possible, it becomes, to fans of the mythos, Mythology Porn.
Simply put, Mythology Porn is the phenomenon wherein the Mythology Gag quotient in a work reaches critical mass. This can be achieved in two ways: first, a creator makes a work which references as many things as possible in a mythos while still telling a completely new story; second, that a creator purposefully creates a new work with the intent to make it THE definitive "omnibus" of the mythos, containing all major plot points, all major characters, all major aspects of mythology, etc., into a single, cohesive story while staying as faithful as possible to the original work.
A good litmus test for whether is a work is Mythology Porn or not is this: if it has so many Myth Gag examples in its trope page that it warrants a separate Mythology Gag subpage, it's Mythology Porn.
Note that this trope is NOT concerned with ACTUAL "mythology porn". Just 'cause it's named this doesn't mean you'll find references of Hercules doing the nasty with Ha Mulan... unless a work somehow manages to do that AND fit the proper definition of this trope at the same time. In which case, carry on.
- Many Elseworld books by DC end up being A-grade Mythology Porn. Given The DCU's penchant for the Crisis Crossover, several Elseworld books are used as a means to create a mini Crisis, and reimagine characters in new ways.
- Kingdom Come is perhaps the crowning achievement in this regard. By its nature - being a dual treatise on the absurdity of The Dark Age of Comic Books, as well as pointing out that rabid fans of The Silver Age of Comic Books need to take off the Nostalgia Filter and admit that Age was far from perfect, as well - it tried to allude to nearly every character of note in DC's immense portfolio. With a cast of over 100 characters, introducing concepts popular enough that they began leeching into the main DC universe (such as Red Robin and the romantic tension between Wonder Woman and Superman), and widely heralded as the mark of the end of the Dark Age and the beginning of The Modern Age of Comic Books, to say its success was spectacular is an understatement.
- Superman: Red Son takes as many concepts from the main DCU as possible and turns them sideways. The entire Justice League, albeit retooled, takes part at various times, major villains Bizarro, Lex Luthor, and Brainiac play pivotal roles in the story, characters such as Lana Lang and Batman get Soviet expys, Lois Lane is present and the Red String of Fate nature of her and Superman's relationship is alluded to (but ultimately averted), and the number of Easter Eggs to be found is dizzying.
- Marvel 1602 is a prime example as well. Being an Alternate Universe of the whole Marvel Universe, it tries to make at least one Mythology Gag per page; some pages are so laden with them that they may take several readings to notice them all.
- The Marvel Cinematic Universe comes off as this. Some movies' basic plots are taken directly from comic story arcs; others are entirely new. But, regardless, the shear number of allusions or Easter Eggs in each movie is enough to incur constant, explosive nerdgasms for longtime Marvel fans. Made especially more egregious because fans wonder what's just a gag, and what's foreshadowing to movies to come.
- This was the intent when T. H. White set to paper The Once and Future King. While it's far from incorporating EVERY story involved in Arthurian Legend, it is one of the most cohesive and complete, especially concerning the rise and fall of Camelot.
- An earlier work, Le Morte Darthur by Thomas Malory, did a better job at incorporating as many fine details of the mythology as possible, though it shows its age by presenting the characters in a far less human light than White's novel.
- The Fengshen Yanyi acts as this for Chinese Mythology. It simultaneously acts as a fictionalized account of the overthrow of the Shang Dynasty by the Zhou Dynasty, and as an origin story for the vast number of gods within the Celestial Bureaucracy, including fan favorites Li Ching, Nezha, and Lei Zhenzhi.
- Cannon Spike is this for Capcom, a game full of Mythology Gags from diverse games of the company, having their protagonists from diverse game franchises and even the original characters are based on certain games.
- Super Smash Bros. Ultimate adds a "Spirits" system in which the spirits of characters not in the game as fighters possess and augment those who are. Nearly every spirit to character to stage match is some sort of Mythology Gag, see Super Smash Bros. Ultimate for the full list.
- Transformers Prime, by design, was meant to incorporate as many aspects of every other Transformers story possible. The idea was to create a single story which would act as THE "truest" Transformers story possible. This was partially achieved not only by flooding the show with plot points and characters from every show thus far, but even going so far as to get the original voices of Optimus Prime and Megatron back into the drivers seats of their characters.