A unicorn pony could be a main character. They already have magical abilities which could be enhanced with Assassin's Creed - like skills. For example, their magic could be used for stealth or to create distractions, much like an assassin would use tools. Another option could be a pegasus pony. Their ability to fly would give them an advantage in terms of mobility, similar to how assassins move around rooftops and in high places in the Assassin's Creed games.
Obviously, Sherlock Holmes would be one of the main characters. He would bring his brilliant mind and unique detective skills to the story. For the Assassin's Creed side, Ezio Auditore could be a great choice. His charm, combat skills, and experience in the assassin world would create an interesting dynamic with Sherlock.
Connor is likely to still be one of the main characters. He was central in the original game and in the rewrite fanfic, his story could be expanded or changed in interesting ways. Haytham Kenway might also be a main character. His relationship with Connor, which was complex in the original, could be further explored in the rewrite. And there could be other characters like Achilles Davenport who play important roles as well, guiding Connor in his journey as an assassin.
In addition to Izuku, there could be his friends from 'My Hero Academia' who somehow get involved in the Assassin's Creed world. For example, Bakugo might end up there too and have a rivalry with Izuku in this new setting. And from the Assassin's Creed side, characters like Connor could be main characters as well, as they interact with Izuku and his friends.
One possible plot could be that a pony discovers an ancient artifact in Equestria that has Assassin's Creed - like powers. Maybe it gives the pony the ability to blend into the shadows like an assassin and jump incredibly high. The pony then has to use these new powers to protect Equestria from an unknown threat that is slowly emerging and wants to take over the magical land.
Most likely Giovanni is one of the main characters, since his name is in the title. But there could also be other characters from the Assassin's Creed universe that interact with him in the story.
Giovanni would obviously be one of the main characters. There might also be other assassins he is associated with, like Ezio. His family members could also be main characters if the fanfic focuses on his personal life.
MLP characters can bring their unique abilities. For example, Applejack's strength could be used in combat situations within the Assassin's Creed world. She could be like a powerful warrior - assassin. Also, Rarity's sense of fashion could be used to create disguises for the assassins. She could design elaborate outfits that would help them blend into different social classes.
In 'Assassin's Creed: Renaissance', Ezio Auditore is a main character. He is an Italian nobleman turned Assassin. His journey from a young man seeking revenge to a master Assassin is really captivating.
A young hacker could be a great main character. They already have skills that would be useful for an Assassin in the modern day, like being able to access restricted information and disrupt enemy systems. They could be drawn into the Assassin - Templar conflict when they stumble upon a secret digital conspiracy.
Altair is undoubtedly one of the most popular characters. As the main protagonist in the game, he has a lot of potential for further development in fanfics. His complex personality, skills as an Assassin, and his journey of self - discovery make him a prime candidate for many different storylines.