One common theme could be captivity. When a character is gagged, it often implies they are in some sort of captivity, either by an enemy or in a situation they can't easily escape. Another theme might be mystery, as the gagged state can add an element of mystery about what the character has seen or knows.
In some fanfictions, Dean being tape - gagged might lead to some character development. He could learn to communicate in other ways, like using his eyes or body language more effectively. This would make him more resourceful and add depth to his character. For instance, he might be able to signal Sam about a hidden weapon or a way to escape just by using his expressions.
In Supernatural fanfiction, a scenario where Dean is clothed and gagged can be used for various storytelling purposes. It could be part of a capture or hostage - like situation created by an antagonist. Maybe a powerful demon has captured him to prevent him from interfering in their evil plans. Writers might use this to build tension and show Dean's vulnerability despite his tough - guy image.
In fanfiction, a tape - gagged Dean might be part of a rescue mission plot. His friends Sam and Cas could be frantically searching for him, and when they find him, they have to deal with the immediate threat while also getting the gag off him so he can communicate. It's a great way to build tension and drama in the story.
One common theme is often Dean in a vulnerable or captive situation which leads to him being gagged. This can be related to the show's themes of danger and the supernatural. Another theme could be the emotional response of other characters, like Sam or Castiel, to seeing Dean in such a state.
A clothed and gagged Dean in Supernatural fanfiction could be a result of a spell. Some dark magic user might have put a spell on him to keep him from speaking incantations or warnings. This would lead to an interesting plot where the other characters have to find a way to break the spell and free Dean.
One popular Supernatural gagged fanfiction might be 'The Muffled Hunt' which has an interesting take on the characters in a rather unique situation. However, finding such specific fanfiction can be a bit tricky as it's a niche concept within the vast Supernatural fanfiction universe.
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.
Dean is almost always going to be in these fanfictions when Sam is gagged. Their relationship is central to Supernatural. Rowena could also be a character. She might use her magic to either gag Sam for her own purposes or to help him if she has a change of heart. And Gabriel. He could turn up and use his trickster abilities to either put Sam in the gagged situation as a joke or to get him out of a more serious one.
You can try searching on fanfiction websites like Archive of Our Own (AO3). There are a large number of 'Supernatural' fanfictions there, and you can specifically search for ones involving Dean being gagged by using relevant tags and filters.