Well, it's hard to say if it's common. It depends on how the characters are portrayed in different scenarios. In some fan-created universes, they might be shown as interested in fanfiction as a form of entertainment or to understand how they are perceived by fans. But in the original or more 'canon' interpretations, there's no clear indication that they would typically read fanfiction.
If they did read fanfiction, Jeff might be interested in ones that show him in a more powerful or feared light. Maybe stories where he outwits the authorities or other killers. As for Laughing Jack, he could be drawn to fanfiction that exaggerates his creepy and manipulative nature, perhaps ones where he has more elaborate ways of scaring his victims.
You can try looking on some fanfiction platforms like Archive of Our Own (AO3). They have a large collection of various fanfictions, and there's a good chance you'll find Jeff the Killer and Laughing Jack Yaoi fanfictions there. Just use the search function and type in the relevant tags.
The yaoi aspect adds a whole new layer. In a normal horror setting, their relationship would be just one of horror and chaos. But in yaoi fanfiction, there can be an exploration of emotions like love, lust, and jealousy. It's interesting to see how these emotions are portrayed within their dark and twisted personalities, and how they interact with each other in a romantic or sexual context, while still maintaining their horror elements.
In this kind of fanfic, the relationship between Eyeless Jack and Jeff is often complex. It might involve elements of an uneasy alliance or a strange form of mutual understanding. Sometimes, they could be portrayed as antagonists who grudgingly respect each other's abilities in a dark and twisted world.
The theme of redemption or lack thereof can also be found. Despite their dark natures, some fanfics may explore if there is any chance for either of them to be redeemed, or if they are doomed to a life of horror and violence forever. This adds a layer of depth to their characters and their relationship in the 'eyeless jack x jeff fanfic'.
One common theme is the exploration of an unusual relationship. Given the nature of the characters, it often delves into the darker aspects of their bond.
One great 'eyeless jack x laughing jack fanfiction' is 'The Unlikely Bond'. It explores their unique relationship in a rather dark and mysterious setting. The author does a great job of creating an atmosphere that makes the reader feel like they are truly in the world of these two characters.
Sure. You can try looking on fanfiction websites like Archive of Our Own. Just search for 'laughing jack x lucy' in their search bar, and you'll likely find a variety of fanfictions written by different authors with different takes on their relationship.
I don't have the exact date for you. But usually, you can try looking up on dedicated horror fiction databases or asking enthusiasts in related online communities to get that information.