Well, in some Supernatural 13x17 fanfiction, there might be a plotline where a side character from that episode gets a more prominent role. For example, they could be the key to solving a mystery that was only hinted at in the actual episode. It could also be about how the events of 13x17 change the future trajectory of the characters' lives in ways that the show didn't explore.
One interesting plotline could be the discovery of a long - hidden power within a main character. For example, Sam might find out he has a unique ability that was suppressed all this time, which changes the dynamic of his relationships with Dean and other characters in the story.
A great plotline would be if Jessica came back as a sort of supernatural being herself. Maybe she was brought back by a powerful witch, but not fully human. This would create a whole new dynamic as Sam would have to deal with her new state. She could be on a quest to find out who brought her back and why, and in the process, she and Sam could rekindle their relationship in a very different way compared to before.
Some fanfictions might focus on the emotional aftermath for Sam and Dean. Maybe Sam is more affected by what happened than he let on in the actual episode, and the fanfiction could explore his inner turmoil. Also, there could be plotlines where other hunters get involved in the events that followed 'No Rest for the Wicked' and how their presence changes the dynamic between Sam and Dean.
One interesting plotline could be Chuck's struggle with his role as God. In some fanfictions, he might question the morality of his actions, like the way he's manipulated the Winchesters' lives. It adds a new layer of depth to his character.
Another plotline might involve a love story within the context of 'Still Breathing' fanfiction. For example, a hunter falls in love with a non - human entity who is also trying to survive in a world full of supernatural threats. Their relationship is tested as they face various challenges together, and they have to figure out how to keep each other 'Still Breathing' in a dangerous world.
One possible plotline could be Gabriel coming back with new powers and a mission to set things right in the Supernatural world. Maybe he teams up with the Winchesters in a way they never expected.
Another interesting plot could be Sam forming a connection with other werewolves. Maybe he discovers a pack that has different values than the ones he's used to fighting, and he has to decide whether to side with them or stay with his hunter ways. This creates a moral dilemma for him. There could also be a plot where Sam's werewolf nature attracts a powerful and dangerous enemy that specifically targets him because of his unique condition. It forces him and Dean to find new ways to protect themselves and defeat the enemy.
One interesting plotline could be their eternal struggle for power in a new, alternate universe created within the fanfiction. They might fight not just physically but also in the realm of manipulating other characters' loyalties.
A plotline could be that on Halloween, Sam and Dean discover a town where every year, people disappear mysteriously. They suspect it has something to do with an ancient Halloween ritual gone wrong. As they dig deeper, they find that a group of cultists are trying to summon a powerful entity. Sam uses his research skills to find a way to stop the summoning, while Dean prepares for a fight.
One possible plotline could be Sam being captured by a villain and gagged to prevent him from using spells or calling for help. Another could involve a prank gone wrong within the Supernatural universe where Sam ends up gagged in a humorous yet tense situation. Maybe there's a plot where an otherworldly entity has the power to silence Sam by gagging him to stop his investigations.