Perhaps it could be a character from Barbie's world who has turned evil. This character could have followed Barbie Pegasus into the Soul Eater world and decides to team up with the local villains. Their combined powers would pose a great threat to both Barbie Pegasus and the Soul Eater characters, and it would be up to them to work together to defeat this new alliance.
The main villain could also be one of the existing powerful enemies from Soul Eater, but with an added twist. For instance, Crona could be influenced by an external force that makes them even more dangerous. And they might see Barbie Pegasus as a threat to their plans because of her unique powers. So they try to stop her from helping the good guys in the Soul Eater world.
Well, it could be about how Barbie Pegasus enters the world of Soul Eater. Maybe she brings some of her magical pony powers into that world. For example, her ability to fly could be really useful in the often dangerous world of Soul Eater.
Another possibility is that Soul could be a main character. His cool and laid - back personality might be intrigued by Barbie. They could have some interesting interactions, especially when it comes to music (since Soul is into music) and Barbie's various talents. And Death the Kid, with his unique OCD and powerful abilities, could also play a major role, perhaps being both annoyed and impressed by Barbie at the same time.
Perhaps it's a story where the aesthetic and positive vibes of Barbie contrast with the darker, more action - packed world of Soul Eater. She might introduce a new way of thinking to the characters in Soul Eater. For example, her fashion sense could influence the way the Soul Eater characters dress, while at the same time, she learns about the importance of protecting souls from them.
Obviously, Barbie would be one of the main characters. And the pegasus, of course. There could also be other characters like Barbie's friends who might be worried about her when she disappears into the pegasus' world. Or there could be some magical creatures in the pegasus' world that play important roles, like a wise old owl or a mischievous fairy.
Maybe the main villain is a mutant who has turned evil and has a grudge against both the wizarding world and normal mutants. He wants to destroy the balance between the two worlds. He sees Harry as a symbol of the wizarding world's power and Logan as a threat to his plans of mutant domination. So he sets out to eliminate them both.
Dr. Eggman could team up with a Pokemon villain like Team Rocket. They could combine their technology and evil plans. Eggman might use Team Rocket's knowledge of Pokemon to capture strong Pokemon and use them in his machines, while Team Rocket could benefit from Eggman's advanced robotics to create more powerful devices for stealing Pokemon.
The main characters include Princess Annika, who is a determined and fearless princess. She is the one who sets out on the journey to save her kingdom. Brietta, the pegasus, is also very important. She helps Annika in her quest and is actually her sister. The evil wizard Wenlock is another key character as he is the source of all the trouble. His actions of freezing the kingdom drive the whole story forward.
Well, perhaps Barbie could be on an adventure in a magical land and meet the pegasus. They might team up to save the land from an evil sorcerer. The pegasus could use its flying ability to help Barbie reach places she couldn't on her own.
The new girl could be a transfer student at the DWMA. She has a unique weapon form that no one has ever seen before. Soul Eater is intrigued by her and wants to learn more about her. They end up being paired for a mission, and during the mission, they discover that they have a lot in common, like their love for music, which helps them bond.
Bellatrix Lestrange is also a likely candidate. Her encounter with Hermione would be extremely intense. Given her loyalty to Voldemort and her rather unhinged nature, she would likely pose a serious threat to Hermione, but Hermione might also find a way to use Bellatrix's madness against her.