It could be that the supernatural elements are out of control, causing chaos and destruction. Or perhaps the main character has a personal crisis that coincides with the supernatural problems, making it a really rough week.
It could be a series of unexpected and dangerous supernatural events that the characters struggle to deal with.
I'm not sure specifically as there could be many different 'a bad week' Supernatural fanfics. It might be about a particularly tough week that the characters in Supernatural, like Sam and Dean, experience. Maybe they face a series of difficult cases, or there are personal problems within the Winchester family during that week.
Fanfiction.net is also a good place to search for it. There are many Supernatural fanfics on this site. Navigate to the Supernatural section and then try to find it either by browsing through the recently updated fics or by using the search bar to look for the specific title 'a bad week supernatural fanfic'. However, the quality of fics can vary on this site, so you may need to read a bit to see if it's what you're looking for.
The combination of two different worlds makes it interesting. 'Bad Company' has its own rough and tough military - like setting, and 'Supernatural' is all about the supernatural elements. When you put them together in fanfic, it creates unique storylines. For example, the Bad Company characters' combat skills can be used in new ways when facing demons or other supernatural beings.
The uniqueness of a 'A Week in Heat Fanfic' might lie in its plot. It could have a very specific and engaging storyline that sets it apart from other fanfics.
It could be that the 'bad name worm' fanfic has no clear direction or goal. Or the dialogues might be unrealistic. Another reason could be that it doesn't stay true to the original concept of 'bad name worm'.
One thing that can make a 'bad Twilight fanfic' is poor writing skills. If the grammar and spelling are constantly wrong, it's really off - putting. Also, when the author completely misinterprets the characters' personalities from the original Twilight series. For example, if Bella is made into a super - confident and outgoing character instead of the introverted one she is in the books, it can feel really wrong.
A lot of things can make a fanfic bad. Maybe the plot is all over the place and doesn't make sense. Or the writing style is choppy and hard to follow.
One factor could be a complete disregard for the established lore and characters in the Harry Potter universe. For example, if a fanfic makes Harry a completely different person with no resemblance to his original character traits, like suddenly making him extremely cruel for no good reason. It just doesn't fit with what we know and love about the series.
One reason could be a lack of understanding of the original Sonic characters. For example, if the author makes Sonic act completely out of character, like being overly mean or cowardly when he's typically brave and heroic in the official games and lore. Another factor might be a really convoluted and uninteresting plot. Instead of an exciting adventure like in the Sonic games, the fanfic might have a plot that's hard to follow and lacks any real action or purpose. Also, poor writing quality such as a lot of grammar and spelling mistakes can make a Sonic fanfic bad.
A bad Warhammer 40k fanfic might have a weak plot. It could be just a bunch of random events strung together without any real purpose or build - up. For instance, the story might start with a battle against the Tyranids, then suddenly shift to a diplomatic mission with the Eldar with no clear connection between the two. Also, bad writing style can contribute. If the prose is overly simplistic or filled with grammar and spelling mistakes, it makes for a not - so - great fanfic.