I'm not entirely sure specifically what that fanfiction is about. It could potentially be about Bill Cipher achieving or obtaining Will Cipher in some way, perhaps in a strange or otherworldly scenario within the context of the Gravity Falls universe. It might involve some sort of power play or a very unique plot device that only fans who have read it would know for sure.
The black candle that Harry gets from Bill in the fanfic could have multiple interpretations. It could be a warning sign. In some magical traditions, black candles can represent danger or negative energy. However, it could also be a source of power. Perhaps in the fanfic's unique magical system, black candles are used to access a certain type of magic that is not commonly used. Another possibility is that it is a plot device to create suspense. The author might use it to make the readers wonder what Harry will do with the candle and what consequences it will bring. It could also be a link to a hidden past or a secret that Bill and Harry are about to uncover together.
Finding specific fanfiction like 'Bill Cipher gets Will' can be a bit of a hunt. Some Discord servers dedicated to Gravity Falls might also be a good source. Members often share their works or know where to find interesting fanfics. However, make sure to follow the rules of each platform when looking for and accessing fanfiction.
It might also be related to a spiritual or religious practice in fictional tales. The stretching could be seen as a way to purify her body or soul, especially if she passed out during a trance - like state. It could be part of a ceremony to revive her and bring her back to a normal state of being in the context of that story's beliefs.
Maybe Harry will be led into a new adventure. The black candle could be a key to unlock a hidden place or a mystery. For example, it could lead him to an ancient wizard's lair where he discovers a long - lost spell or artifact.
One possible scenario could be in a medical context. Maybe she passed out due to an accident or a medical condition, and the stretching is part of a physical therapy or rehabilitation process. For example, if she had a muscle injury or a joint problem, gentle stretching might be done to improve her range of motion and aid in her recovery.
Since we only have the title 'bill's new frock story', it's difficult to say exactly who Bill is. He might be a fictional character created by the author. Maybe he's a young boy or a man who has a particular interest in fashion, which is why the story focuses on his new frock. Or he could be a character in a specific setting, like a small town where everyone knows each other and his new frock becomes a topic of conversation.
I'm not sure who exactly 'Bill Harvey' is just from 'Bill Harvey End of Story'. It could be a specific person known within a certain community, family, or a character in a very niche story or event that I'm not familiar with.
If the 'Wild Bill' in 'Wild Bill the True Story' is not Hickok, it could be some other local hero or character. There were many people in history with colorful nicknames. This 'Wild Bill' could be someone who had a significant impact on the community where the story is set, perhaps a man who fought against injustice, or who had some remarkable feats that made him stand out in the local lore.