Another way is through the use of the show's locations. They know about the bunker, the various haunted places, etc. By setting their fanfiction stories in these familiar locations, they are incorporating their knowledge. They can also add new details to these places, but still keep the essence of what the locations mean in the context of 'Supernatural'.
Writers often have Flash use his speed in creative ways. For example, in some fanfictions, he can run around an enemy so fast that he creates a vortex, which the Avengers can then use to their advantage. His speed also allows him to quickly gather information or deliver objects across long distances in an instant.
Some writers simply drop in words from the existing Harry Potter languages like spells or the names of magical objects. For example, they might use 'Accio' when a character needs to summon something. Others might create new phrases within the language framework. They could make up a new incantation for a made - up spell.
In some fanfictions, Naruto's ability to sense chakra is combined with Nami's knowledge of the sea. Naruto can sense the presence of powerful sea creatures or hidden enemies underwater by detecting their unique 'chakra - like' energy. Nami, on the other hand, uses her navigation skills along with Naruto's sense of direction (which is enhanced by his ninja training) to find hidden islands or treasures. They work together, with their abilities complementing each other in unexpected ways.
Writers often use the concept of different planets having unique species. For example, they might create a water - covered planet in the Star Wars universe where mermaids exist. They then blend the mermaids' natural abilities like swimming and communication underwater with the Star Wars elements such as the Force and spaceships.
Writers often create new spells that are related to lightning. For example, they might come up with a spell like 'Fulguratio' which shoots out a bolt of lightning. They also use it to enhance the power of existing characters. Imagine Harry Potter suddenly being able to control lightning in addition to his other powers. It would make him even more formidable. Some writers might also make lightning magic exclusive to a certain group or family within the wizarding world.
In Cardcaptor Sakura crossover fanfictions, when incorporating different universes, writers look at the character traits. For instance, if it's a crossover with the world of Fullmetal Alchemist. Edward Elric's determination and Sakura's kindness could be used to create a bond between them. They also think about the power systems. If Sakura crosses over to the world of One Piece, her card magic could be compared to Devil Fruits powers. Writers might also use the concept of alternate dimensions. Like Sakura accidentally falling into the world of Digimon through a dimensional rift and then having to find her way back while helping the Digidestined.
Some writers use the concept of shared threats to bring the two universes together. In a harem fanfic, this means that both Naruto and Resident Evil characters have to face a common enemy. This enemy could be a powerful being that combines the abilities of the T - virus from Resident Evil and the power of the tailed beasts from Naruto. As they fight together, the relationships in the harem develop, with characters learning from each other's strengths and weaknesses.
Writers might use the 'lemon' as a symbol. For example, it could represent something sour in their relationship, like a misunderstanding that needs to be resolved. So, when Percy and Neptune have an argument, the presence of lemons or lemon - scented things in the scene can enhance that feeling.
Writers often use the unknown identity of the father as a mystery. If it's a new character in the fanfic, the readers are left guessing about who he could be. Also, they might make the pregnancy itself a mystery, like it's a result of some strange experiment or a hidden encounter. Another way is to make the safety of the pregnancy a mystery. With all the villains in the Detective Conan world, there could be threats to the pregnant character that need to be uncovered.
Writers often have Inner Moka use her vampire strength and speed in combat situations in the Naruto universe. For example, in some fanfics, she can quickly dodge attacks like a ninja but with her own vampiric grace. Naruto's ability to use chakra and his shadow clone jutsu can be combined with Moka's powers. Like in a story where Naruto creates clones and Moka uses her vampire senses to guide them in a battle.