Perhaps a fanfiction where Doctor Strange loses his powers and has to rely on his wits and the knowledge of ancient spells he has memorized to defeat a powerful enemy. This would show his growth not just as a sorcerer but as a person. For example, he could use his medical knowledge in combination with some basic magical principles to outsmart the foe.
A story where Doctor Strange has to train a young and unruly apprentice. The apprentice has a natural talent for magic but lacks discipline. Doctor Strange has to not only teach the apprentice how to control their powers but also instill in them a sense of responsibility, all while dealing with various threats to the magical world that are attracted to the apprentice's untamed power.
One idea could be Doctor Strange accidentally sends the Avengers into an alternate dimension where magic doesn't exist and they have to find a way back using only their non - magical skills. Another could be that an ancient evil forces Doctor Strange to choose between sacrificing the Avengers or the entire world. Or perhaps a spell gone wrong makes the Avengers swap powers with each other, and Doctor Strange has to fix it while also dealing with an incoming threat.
One idea could be that they team up to face a new, powerful interdimensional threat that neither can handle alone. Maybe a villain has found a way to merge different dimensions in a chaotic way, and Iron Man's tech and Doctor Strange's magic are needed to stop it.
One idea could be that you insert yourself as a new apprentice to Doctor Strange. You could start with little magical knowledge and learn from him, facing challenges like protecting the Sanctum Santorum from minor demons. Another could be that you are inserted into the story during the time when Strange is facing a powerful enemy and your unique modern - world knowledge helps him in an unexpected way, like using technology to enhance a spell.
One idea could be that Doctor Strange accidentally opens a portal to the wizarding world of Harry Potter. He could end up at Hogwarts and be mistaken for a new kind of wizard. Maybe he tries to use his magic to teach the students some new spells or ways of magic, but it causes chaos because his magic is so different from theirs. For example, his use of the Time Stone could mess with the time - turners at Hogwarts.
Perhaps a time - travel based fanfiction. Christine accidentally gets sent back in time to a period when Doctor Strange was just starting to learn magic. She has to find a way to get back to her own time, and in the process, she ends up changing some events in Strange's past that have unforeseen consequences for their present relationship. Strange has to use his growing magical powers to fix things while also dealing with his feelings for Christine.
One idea could be that Doctor Strange discovers he is pregnant due to some strange magical experiment gone wrong. His powers start to fluctuate in unexpected ways as his body adjusts to the pregnancy. He has to deal with the reactions of his fellow sorcerers, some of whom are shocked and others who try to help him manage his new condition while still protecting the world from magical threats.
One plot idea could be Doctor Strange traveling back in time to prevent a certain spell from being misused in the past that led to a dark future. He could face challenges like encountering his past self who doesn't believe him at first.
One idea could be that Sherlock's deductive skills are needed to solve a mystery in the magical world of Doctor Strange. Maybe a powerful artifact has been stolen and Sherlock's unique way of seeing details helps find it. Another could be that Doctor Strange uses his magic to transport Sherlock to different dimensions to solve a case that spans across realities. For example, a serial killer who can move between dimensions and Sherlock has to use Strange's magic to track him down.
Another plot could revolve around an alternate timeline where Sean didn't have his powers. How would they deal with the situations they faced in the game? They might have to rely more on their wits and the kindness of strangers. This could lead to a whole new set of challenges and character developments. For example, Sean might become more street - smart in a different way compared to when he had his powers.
One idea could be that a magical rift opens up between the Harry Potter universe and the Marvel universe where Hermione and Doctor Strange meet. They could team up to close the rift which is causing chaos in both worlds. Strange uses his magic to hold off the magical creatures spilling into the Marvel world while Hermione uses her vast knowledge of spells to find a way to close it from her side.