One idea could be a crossover with 'Grey's Anatomy'. The Good Doctor's Dr. Shaun Murphy could visit Grey Sloan Memorial Hospital. He could collaborate with the doctors there on a complex surgical case. Maybe there's a patient with a very rare condition that requires Shaun's unique perspective and the surgical skills of the Grey's doctors like Meredith Grey.
How about a crossover with 'ER'? Shaun could be part of a team dealing with a mass casualty event. He would have to work quickly and efficiently with the ER doctors. This could also be a chance for him to learn from their experience in handling high - stress emergency situations and for them to learn from his in - depth medical knowledge.
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.
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.
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.
One idea could be a story where Melendez and Claire are paired on a complex medical case that forces them to rely on each other in new ways. They might have to work outside of their comfort zones and in the process, their relationship deepens as they learn more about each other's medical instincts and personal strengths.
One plot idea could be that Aziraphale and Crowley from Good Omens get dragged into a case that the Winchester brothers are investigating in Supernatural. Maybe it's a demon that's a bit too powerful for Sam and Dean, and they need the help of the angel and demon duo who have a different approach to dealing with the supernatural. Another idea is that the two universes' versions of Heaven and Hell start to merge, and characters from both shows have to figure out how to stop it while also dealing with their own personal issues.
One idea could be a crossover with 'Wizards of Waverly Place'. The Russo family could visit the Duncan family in Good Luck Charlie. Maybe Alex Russo accidentally uses magic in front of the Duncans and chaos ensues as they try to cover it up. Another plot could be a crossover with 'Hannah Montana'. Miley Stewart could come to town for a concert and meet Teddy. They could bond over their experiences of growing up in the spotlight, with Teddy sharing her video diary experiences and Miley sharing her pop star life.
One plot idea could be that the characters from Good Omens and Homestuck find themselves in a shared alternate universe. The angels and demons from Good Omens might be quite confused by the strange and complex world of Homestuck, while the Homestuck characters could be intrigued by the celestial beings. For example, Crowley could team up with a Homestuck troll to outwit some overzealous angels. Another idea is a crossover where they have to solve a mystery that spans both their universes. Maybe a powerful artifact has been stolen and its pieces are scattered across both worlds, forcing the characters to cooperate despite their differences in nature and origin.
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.
Maybe a crossover with a magical anime. The nanbaka characters could suddenly find themselves in a world full of magic. Some of the nanbaka characters might be really good at using magic in unexpected ways, like Jyugo using his shackles in a magical battle.
A crossover with a modern - day action story could be really cool too. Spartacus and his crew could be brought to the present day through some time - travel mishap. They then have to navigate the modern world, learning about new weapons and technology. They could use their ancient fighting techniques in modern combat situations, like taking on a powerful criminal organization.