One idea could be a crossover with 'The Lord of the Rings'. The Skeksis could be interested in the power of the One Ring and try to get it from Frodo. This would create an epic battle between the good forces of Middle - earth and the evil Skeksis. Another idea is a crossover with 'Star Wars'. The Gelfling could be like the Jedi, with their own special powers and connection to a kind of 'Force' in the Dark Crystal universe. They could team up with the Jedi to fight against a common enemy.
You could write a 'the dark crystal fanfiction' about a Skeksis who has a change of heart. Perhaps this Skeksis realizes the error of their ways after seeing the destruction they've caused. They then try to secretly help the Gelflings, all while hiding their new - found compassion from the other Skeksis. This would add an interesting layer of drama and conflict to the story.
A possible plot for Dark Crystal human fanfiction is a human scientist who is researching parallel universes and accidentally crosses over into the world of the Dark Crystal. This scientist then tries to study the unique ecosystem and magic of Thra. Along the way, they get involved in the political and social struggles of the Gelflings and Skeksis. They might try to use their scientific knowledge to find a way to stop the Skeksis' tyranny and help the Gelflings reclaim their rightful place in Thra.
One idea could be a crossover with the Harry Potter universe. Sailor Moon and her friends could attend Hogwarts and have to deal with both magical threats from the wizarding world and the dark forces they usually face. For example, they might help the students at Hogwarts fight off a new kind of dark magic that has similarities to the dark energy they combat in their own world.
Another interesting fanfiction idea would be to have a character from The Dark Crystal, like Jen, end up at Hogwarts. Jen could learn about magic and how it differs from the magic in his own world. He might form friendships with the Hogwarts students and together they could face a common threat that somehow links the two universes, like a dark force that wants to take over both the wizarding world and the world of The Dark Crystal.
One idea could be exploring the backstory of a minor Gelfling character. Maybe they have a secret connection to the Skeksis that they're trying to hide. Another could be a story about Gelflings from different clans coming together to form an even stronger resistance before the events of the show. And a third could be a fanfiction where a Gelfling discovers a new power within themselves that could potentially turn the tide against the Skeksis.
One idea could be a crossover with 'The Lord of the Rings'. Picture the Dark Souls characters in Middle - earth, facing off against orcs and other dark creatures. Another could be a crossover with 'Bloodborne'. The gothic and nightmarish settings of both could blend well, with hunters and Dark Souls' warriors teaming up against a greater evil. A third idea might be a crossover with 'Final Fantasy'. The different magic systems and character classes could create really unique and exciting storylines.
A crossover with 'Final Fantasy' would be cool. The magic systems in both could be combined in interesting ways. For example, a Dark Souls 2 mage could learn some spells from a Final Fantasy character. Also, a crossover with 'The Elder Scrolls' series. The vast open worlds of both could create an amazing setting for the fanfiction. The character could explore different regions of Tamriel and use their Dark Souls 2 abilities to survive.
One idea could be that the vampires in Buffy's world somehow cross over to the Dark Angel universe and the transgenic characters have to deal with them. They might initially mistake vampires for some new kind of transgenic experiment gone wrong. Another idea is that Buffy herself travels to the Dark Angel world and teams up with Max to fight against a common enemy that is threatening both of their worlds, like a powerful demon that has found a way to use transgenic technology for evil purposes.
One interesting concept could be the exploration of human - Dark Crystal world interactions. Maybe humans are trying to understand the unique magic or power systems in the Dark Crystal universe.
One idea could be that a case in NCIS leads them to discover a secret project related to the genetic experiments in Dark Angel. Maybe they find a link between a murdered Navy officer and a group trying to recreate the transgenic experiments. So, the NCIS team has to work with Max from Dark Angel, who has her own knowledge and skills in this area.