In a crossover with the Mortal Kombat universe, characters like Scorpion or Sub - Zero could be added. Their unique fighting styles and powers would add a new dimension to the Avengers' battles. Another character could be Goku from Dragon Ball Z. His super - strength and ability to fly and use energy blasts would make for some exciting interactions with the Avengers.
One unique character for 'avengers multi crossover fanfiction' could be Sonic the Hedgehog. His speed would be a great asset to the Avengers in combat situations. Also, in a crossover with the Final Fantasy series, Cloud Strife could be added. His Buster Sword skills and his experience in fighting against powerful foes would be a great addition to the Avengers' roster.
Hermione Granger from the 'Harry Potter' series could be an interesting addition. She could use her magic knowledge to help the Ghostbusters understand the more esoteric aspects of the ghosts they're dealing with. Maybe she could even develop spells that work in tandem with the Ghostbusters' technology.
A character like a Pokémon whisperer who can communicate with Pokémon on a deeper level than anyone else. This person could teach Ash new ways to bond with his Pokémon. Another could be a wandering minstrel who travels around the Pokémon world, singing tales of legendary Pokémon and has clues about a powerful Pokémon Ash is seeking.
A character who is a master of shadow puppetry, but not in the normal sense. Instead of just creating simple shapes, they can create entire landscapes and armies of shadow creatures. This character could have a mysterious backstory and their own motives, which could either make them an ally or an enemy in the fanfiction.
A psychic human. This character could sense the demons' movements and intentions before they attack. They could use their powers to help the Doom Slayer or other marines, for example, by warning them of an ambush or guiding them through a maze - like area filled with demons.
A young artist from a neighboring kingdom could be introduced. He hears about the Beast's castle and is intrigued by the rumors of its beauty and mystery. When he arrives, he could befriend Belle and see the relationship between her and the Beast. His unique perspective as an artist could add a different dimension to the story, like he could paint pictures that somehow affect the curse.
Lex Luthor would be an obvious choice. His complex relationship with Superman could add a lot of drama. Also, Supergirl could make an appearance. She could team up with Superman to fight a common enemy while also bonding with Lois as another strong female character.
One character that would be great to add is a time - traveling adventurer. This character could accidentally bring Billy and Mandy to different time periods. They could end up in the prehistoric era, where they meet dinosaurs and cavemen. Or they could be in the future, in a world full of high - tech gadgets that they don't understand. The time - traveling adventurer could then be their guide through these strange times, while also having his own motives and secrets.
In a crossover with 'Star Wars', Luke Skywalker could be a great addition. He could teach the boys about the Force and they could go on a mini adventure together. Also, Princess Leia could be added. She could bring her leadership and strong - willed nature to the group. They could all work together to fight off some Imperial threats that somehow end up in their world.
In a crossover with 'Final Fantasy', Cloud Strife could be added. He is a skilled warrior with a cool sword. He could join Spyro in his adventures and offer his combat skills against powerful enemies. Their different fighting styles, Spyro's magic and flight and Cloud's swordsmanship, would make for an interesting dynamic.
The Doctor from 'Doctor Who' would also be a great addition. With his time - traveling TARDIS, he could bring the characters of Journey to the West to different time periods and planets. He could also help them with his vast knowledge and advanced technology when they face difficult situations, like when they need to break a powerful spell that is beyond their normal capabilities.