Darths & Droids is about roleplayers playing a tabletop RPG following the basic plot of the Star Wars movies, but the notes on strip 50 have specifically stated that there is no Star Wars in the universe where they are. They then extrapolate on how that would impact things such as Mark Hamill's and Harrison Ford's careers, Spaceballs, the fate of sci-fi in media, and finally what the webcomic Darths & Droids would be parodying instead of Star Wars: Harry Potter.
On top of that, that very sentence links to a sample page from that alternate universe Harry Potter strip, which includes a full site layout, cast page, FAQ, and a (non-explorable) archive complete with 50 strips of punny stip titles. Then, when the main strip # 100 was released, this page was silently edited with the same extrapolation on a world where Harry Potter never existed, complete with a link to a The Sound of Music comic with the same bells and whistles. The process repeats every 50 strips, going through X-Men, Aliens, The Wizard of Oz, 300, Avatar, Terminator, Jaws, Casablanca, The Muppet Movie, Inception(appropriately enough), Pirates of the Caribbean, Futurama (despite - orprobablybecause - one of the lines being "* is known (barely) for doing voiceovers for poorly selling computer games, but gains widespread fame after his appearance in the first Futurama movie.") and now Willy Wonka and the Chocolate Factory. Given that we're still partway through Episode IV, by the time Darths & Droids is finished, the innermost world will be very culturally poor indeed.
On the other hand, once you get deep enough into the recursion, the outer layers could actually start reappearing, and the entire thing could come full circle. After all, there's no reason why Star Wars couldn't exist in a world where the characters are playing a home-brew RPG based on 300. In fact in the world where the Comic Irregulars are making a screencap comic based on Pirates of the Caribbean, it is stated that Keira Knightley is known primarily for her role in The Phantom Menace.
The final layer will be the first Futurama movie everyone starred in.
Star Wars already exists in the Sound of Music RP 'verse, if the titles are anything to go by (It's a von Trapp!).
Problem is, we're the outermost layer. What story are our roleplayers acting out?
Of course the 300, Avatar and Inception ones, being based on recent movies, are more forced/less accurate than the previous ones (Avatar's nonexistence led to Titanic not existing?).
David Willis makes occasional appearances in Shortpacked! and has an ongoing rivalry with Ethan regarding the Transformers Wiki. He even rented out the store to propose to his girlfriend.
Ashe Rhyder's Roommates fancomic completely reverses this trope. Both the movies/books and the characters from them exist. The characters often watch their own movies, mention their actors, or refer fan service.
Jareth: "Wait. Javert... When the hell did you get so bloody tall?!" Javert: "As it turns out, Quast is tall. Bet you wish Bowie wasn't so short."
And then there's Devious Gingers, an in-universe tv show starring some real actors. Some of those actors play characters who have appeared in the comic.
ThisMénage à 3 Strip: the authors of the comic, as authors of their other comic selling merchandise for it.
An The Order of the Stick comic has a semi-canonical episode where Gary Gygax appears in the afterlife, meeting with Roy. Since this is a world in which Dungeons & Dragons and Gygax do not exist, but which is heavily based on D&D (a specific edition of it, no less) to the extent that characters talk about experience points and +1 swords, this is... confusing.
