Perhaps a story where a character discovers a long - forgotten magic that has been dormant since the very beginning of the vampire lore in this universe. This magic could be the key to solving a major problem like a new, more powerful type of enemy that is threatening both the vampires and the humans in Mystic Falls. The character then has to embark on a journey to fully understand and master this magic.
One idea could be exploring the backstories of the lost boys in more detail. Maybe one of them has a hidden connection to a character from the outside world. Another plot could involve a new villain coming to Neverland who has a different kind of magic that challenges Peter Pan. Also, a story about Wendy's granddaughter returning to Neverland to find a lost family heirloom could be interesting.
A new character could be the main character as well. This new character could be a human who is suddenly thrust into the vampire world in a 'once upon a time' way. They could be the one to bring a fresh perspective to the story, seeing the vampires and their lore from an outsider's point of view and having to learn quickly to survive.
One idea could be that Sora and his friends get transported to the Once Upon a Time realm. They could team up with Emma Swan to fight against the Heartless that start to invade Storybrooke. Maybe the Keyblade can be the key to unlocking some of the dark secrets in the town's past.
Another interesting plot could be Loki falling in love with a character from Once Upon a Time. Maybe he has a relationship with a princess or a powerful sorceress, and their love story is filled with magic, drama, and challenges as they come from different worlds.
One idea could be a new agent arriving at Warehouse 13 with a mysterious past that turns out to be linked to an artifact that was thought to be lost forever. This new agent might unknowingly hold the key to controlling the artifact's power, causing a stir among the existing agents as they try to figure out how to handle the situation.
A love - interest plot for Gideon would also be interesting. He could fall in love with a character from a different realm within the Once Upon a Time universe. Their relationship would be complicated by the different rules and cultures of their respective realms. They would have to overcome many obstacles, like disapproving family members or the threat of war between their two realms.
One idea could be exploring Gothel's backstory before she became the villain we know. Maybe she had a tragic love in her youth that turned her bitter. Another plot could involve Gothel teaming up with an unexpected character from the Once Upon a Time universe, like a hero who thinks they can reform her. A third option is to create a story where Gothel has a daughter of her own and we see how she raises her in contrast to how she treated Rapunzel.
One idea could be to create a story where a new character, an aspiring actress, befriends Rick Dalton and Cliff Booth. She gets involved in their crazy Hollywood adventures and helps Rick revive his career in an unexpected way, like by introducing him to a new type of movie role that suits his acting style better.
Maybe they could time - travel back to a crucial moment in the Once Upon a Time story and change something that has a big impact on their relationship. For example, they prevent a dark curse from being cast which in turn allows them to have a more positive start to their relationship.
One plot idea could be that Hook and Wendy team up to find a magical artifact that can save Neverland from a dark curse. Along the way, they face many challenges and start to develop a deeper understanding and respect for each other.