Sometimes, Dean is taken hostage by a powerful demon who has a vendetta against the Winchesters. This can lead to a complex plot where Dean has to use his wits and any resources he has at his disposal to escape or hold out until Sam arrives. There might also be elements of Dean making deals or trying to outsmart the demon.
Sometimes, in these fanfictions, Dean is secretly married to a supernatural being. For example, he might be married to a fallen angel. This creates a whole new set of problems as he has to deal with the politics and power struggles within the supernatural world while keeping his marriage a secret from Sam and the rest of the hunting community. It can also lead to some interesting character development as Dean has to navigate his feelings for this other - worldly being and his loyalty to his family.
There are often plotlines where the reader is transported into the Supernatural universe and immediately runs into demon dean. Their relationship starts off rocky, with dean seeing the reader as an easy target or a nuisance. But as the story unfolds, they discover that they are linked in some way, perhaps by a prophecy or a shared past life. This leads to a journey of self - discovery for both of them as they figure out their relationship and their roles in the supernatural world.
You can try websites like Archive of Our Own (AO3). It has a large collection of fanfiction, including many about Dean in hostage situations in the Supernatural fandom. Just use the search function to look for relevant tags.
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.
Another plot could be Dean falling in love with an angel. In the Supernatural world, relationships between hunters and angels are complex. So, a fanfiction might explore how Dean's tough hunter exterior softens as he falls for an angel, and how they navigate the differences between their two worlds.
I would say it's not common. 'Supernatural' fans usually discuss their favorite episodes, the relationships between characters like Sam and Dean, or the various supernatural creatures in the show. Fanfiction is a big part of the fandom, but this phrase seems rather odd and not something you'd hear often. Most fan talk is more about the show's official content and how it relates to the fan - created works in a more general sense.
One common theme is brotherly love. Since 'Supernatural' is centered around the Winchester brothers, many fanfictions explore the deep bond between them even further. Another theme could be the fight against evil. Dean is often portrayed as a strong fighter, so stories might focus on his battles.
Another theme is sacrifice. Given the nature of the Supernatural world, they often put themselves in harm's way for each other. Fanfictions play on this selfless aspect of their relationship. For example, Cas might sacrifice his grace to save Dean, or Dean might risk his life to rescue Cas. It shows the depth of their bond.
Common themes in dean and jack supernatural fanfiction include power and its consequences. Jack has a great deal of power, and in these fanfictions, we often see how he and Dean deal with the implications of that power. Another theme is acceptance. Jack is not fully human or fully angel, and Dean has to come to terms with that. There is also the theme of sacrifice. Both characters are willing to sacrifice for the greater good, and this is often explored in the fanfictions, showing how far they will go to protect each other and the world they live in.
Another theme is the exploration of identity. The intersex aspect of the character brings a new dimension to their identity within the Supernatural world. It could be about how they fit into the world of hunters, demons, and angels. In some fanfictions, the intersex character discovers new powers or abilities related to their unique identity.