Definitely Regina from OUAT. Her complex past as the Evil Queen and her journey towards redemption would be fascinating in the context of the 'Descendants' world. She could interact with the villain kids and perhaps offer them some wisdom from her own experiences of trying to break free from her dark past.
Mal from 'Descendants' would be really interesting in a crossover. She has that edgy, rebellious nature but also a good heart. Meeting characters like Snow White or Charming from OUAT could be a great contrast. Mal could learn about different kinds of heroism and leadership from them, and they could be intrigued by her unique way of handling the 'villain' side of her life.
Anthony Bridgerton would be a great character to include. His strong sense of family and his often stubborn nature could lead to some interesting clashes in a crossover. Say, in a crossover with a fairytale world like Cinderella. He might initially be against the idea of the Bridgerton family getting involved with the magic and 'foolishness' of the fairytale world, but then gradually change his mind.
Darth Vader would be an amazing character to include. His imposing presence and incredible power would be a huge threat in the MCU. He could face off against Thor, with their different types of powers creating an epic battle. Another interesting character would be Kylo Ren. His conflicted nature could add an interesting dynamic, especially if he interacted with characters like Captain America who have strong moral compasses.
Definitely Nigel Marven from 'Prehistoric Park'. His knowledge and enthusiasm for prehistoric animals would make him a key figure in any crossover. If it was a crossover with 'Terra Nova', he could team up with the Shannon family. His expertise would help them better understand the prehistoric world they are living in and he could also learn from their experiences in a colony in a prehistoric environment.
The Prophet of Truth from Halo could also be an interesting addition. His devious plans and manipulative ways could create a lot of chaos in the Fallout universe as he tries to gain power over the different factions and their resources.
Ash Ketchum would be a must - include. Imagine him using his knowledge of Pokemon to master Beyblade battles. Also, Gary Oak could be his rival in this new form of combat. From the Beyblade side, Tyson could be an interesting addition. He could bring his Beyblade skills and learn about Pokemon. And of course, Pikachu as a character - like presence in the form of a Pikachu - themed Beyblade would be really cool.
For the PJO side, Nico di Angelo could be a great character. His control over the dead could have some really strange and interesting interactions in Skyrim, where there are also undead creatures. On the Skyrim side, Ulfric Stormcloak or Elisif the Fair could be included. Elisif's leadership and Ulfric's military might could be factors when dealing with the demigods. If the demigods get involved in the civil war in Skyrim, their powers could completely change the balance of power. And Luke Castellan from PJO could also be an interesting character to bring in, as his complex personality could add a lot of drama to the crossover story.
Ra, definitely. As the sun god, he has an almost unlimited source of power. In a crossover with a sci - fi universe, his power could be seen as some kind of advanced energy source. He could also be a very important figure in a crossover with a world of elemental magic, as he represents the sun, which is a huge source of heat and light. Bastet would be another interesting character. Her cat - like nature could make her very adaptable in different crossovers. In a world of pirates, she could be like a ship's mascot with some hidden powers. And Thoth, the god of knowledge. In a crossover with a detective or mystery world, he could use his knowledge to solve complex cases.
Tattletale from 'Worm' could be an extremely interesting addition. Her power of hyper - awareness and her devious nature could make for some really intense interactions with the characters in 'Persona 4'. She could either be a great help in solving the Midnight Channel mystery or a major obstacle, depending on her motives.
Alfred Pennyworth could be an interesting addition. He could offer his wisdom and support to Batman while also being a bit of an outsider in Smallville. His butler skills might come in handy in some unexpected ways, like helping Clark's family with some domestic issues while Batman is out on a mission, and his dry British humor would add a unique touch to the story.
Daniel Jackson from Stargate. He has a deep knowledge of ancient cultures and languages. In a crossover, he could study the origin of the Highlander's immortality, believing it to be related to some ancient alien civilization. His inquisitive nature would drive the story forward as he tries to understand the Highlander phenomenon.