Dante is a very likely character. His flamboyant and confident personality would make for an interesting contrast in the MLP world. He could be the one who brings a different kind of action and chaos to the usually peaceful pony lands.
Vergil would also be a great addition. His more brooding and power - hungry nature could create a lot of tension. Maybe he would be on a quest for some sort of power in the MLP universe that the ponies have to stop him from obtaining.
Well, one interesting concept could be the fusion of the dark and edgy style of Devil May Cry with the colorful and magical world of My Little Pony. Maybe it involves characters from Devil May Cry having to adapt to the more positive and harmonious environment of Equestria. For example, Dante might find himself in a situation where he has to use his combat skills in a non - violent way to solve problems in Ponyville.
Well, it could be Neville Longbottom. He was often seen as a bit of an underdog in the original series, and in a 'Stupid Wizards' fanfic, he could be the one to show that the so - called stupid wizards have hidden strengths. For instance, his knowledge of herbology could be used in a really unique and unexpected way.
Obviously, Harry Potter himself would be a central character. Ron and Hermione, his closest friends, would also likely be in it. Ginny, as Harry's love interest, would probably play a significant role too. Other characters like Neville, who has grown into a strong wizard, could also be featured. And of course, we might see some of the old Hogwarts professors, perhaps McGonagall still guiding the school in some way.
The Marker in Dead Space is also likely to be a key element in a crossover fanfic. It has such a powerful and mysterious presence in the Dead Space universe. In a crossover with a horror - mystery series, the Marker could be the source of all the strange happenings, and characters from both universes would have to figure out how to deal with it or stop its influence.
Princess Celestia is also commonly included. Since it's a Canterlot wedding, as the ruler of Canterlot, she would play an important role in the organization and significance of the event. She could be shown making important decisions regarding the wedding.
Obviously, Rarity herself is the central character. Her friends from the Mane Six, like Twilight Sparkle, who could help her understand the magic involved in becoming an alicorn. Also, Spike might be there, as he's always around Twilight and could play a role in Rarity's journey, perhaps by providing some useful information he's found in his library duties.
Definitely Commander Shepard from Mass Effect. He/She is the central character in Mass Effect and would be a natural fit to interact with XCOM forces. Also, XCOM's Central Officer or top - ranking soldiers could be prominent. They could be the ones making decisions on how to deal with Mass Effect threats or form alliances.
Tony Stark could also be a key figure in some fanfics, even though he's no longer alive in the main MCU timeline. His intellect and previous experiences with multiversal - related events (like in Endgame) could be explored in the fanfic. Maybe the Avengers find a way to access his knowledge or even a version of him from another universe to help them out.
A powerful ancient demon that has been sealed away for centuries could be a great villain. This demon could have the power to manipulate time and space, which would make it a formidable foe for both Dante and Bayonetta. It could be awakened by some dark magic ritual gone wrong in both of their worlds, and its goal could be to merge the two worlds into a chaotic realm of darkness where it can reign supreme.
Percy Jackson himself, of course. And Annabeth Chase. They're like the main duo.