There are fanfictions where Sam and Dean Winchester find themselves in the world of 'Criminal Minds' and have to work with the agents to solve cases that seem to have a supernatural undertone. For instance, a case where victims are found with strange symbols on them, which the BAU initially thinks are just the work of a deranged human, but the Winchesters recognize as signs of a demon's presence. This creates an interesting dynamic as the two groups with different worldviews and methods try to solve the mystery together.
A really interesting crossover fanfiction could be set in a small town. The 'Criminal Minds' team is called in to investigate a series of murders that seem to have a pattern related to local folklore. Unbeknownst to them, the local lore is actually based on real supernatural events. The Winchesters arrive in town separately, also on the hunt for the same supernatural entity causing the murders. Eventually, they cross paths and must combine their skills to stop the killer.
One great example could be a story where the Winchester brothers from 'Supernatural' team up with the BAU team from 'Criminal Minds' to hunt a supernatural - themed serial killer. Maybe the killer is using some dark magic to commit murders and leave no trace in a normal way, so both groups' expertise are needed.
One great example could be a story where the characters from Psych have to team up with the BAU from Criminal Minds to solve a serial killer case that has elements of both the light - hearted mysteries Psych usually deals with and the dark, psychological ones Criminal Minds is known for. For instance, the psychic 'abilities' of Shawn Spencer from Psych could be used in an unexpected way to help the BAU profile the killer.
One great storyline could be where the BAU team is called in to profile a suspect who has a connection to some strange Stargate - related technology. Maybe the suspect is using alien tech from the Stargate universe to commit crimes in the Criminal Minds world. For example, a device that can manipulate minds, which makes it very difficult for the BAU to figure out the true motives.
A great Sherlock and Criminal Minds crossover fanfiction often has well - developed characters from both shows. The writers need to capture the essence of Sherlock's deductive skills and the profiling abilities of the Criminal Minds team. For example, a scene where Sherlock and Reid exchange ideas about a case would be really interesting.
One great plot twist could be when a character from Criminal Minds, like Reid, discovers he has some latent supernatural ability in the crossover world of Supernatural. Maybe he can suddenly see ghosts, which turns the whole investigation in a strange new direction.
Writers should focus on the character interactions. The BAU agents are highly intelligent and scientific - minded, while the Winchesters are more rough - around - the - edges hunters. This contrast can create great tension and also moments of growth and understanding. For instance, Dean might initially clash with Reid over their different beliefs, but as they work together on a case, they start to respect each other's skills. Also, creating a unique and menacing villain that requires both the profiling skills of the BAU and the supernatural knowledge of the Winchesters is key to a compelling story.
One idea could be that the BAU team is called in to investigate a series of strange disappearances that seem to be related to a haunted location that Teamiplier has explored in one of their videos. The two groups initially clash due to their different approaches, but then they start to work together and combine their skills to solve the mystery.
A prevalent theme is redemption. In Criminal Minds, some criminals may seek redemption or the team tries to understand if there's any chance of it. In supernatural fanfic, a character who has made mistakes in the past might try to make up for it. Also, the theme of sacrifice. The characters in both might have to sacrifice something for the greater good, whether it's their safety in Criminal Minds or their powers in a supernatural setting.
I would recommend 'Supernatural Minds: United'. In this fanfic, the hunters from 'Supernatural' team up with the BAU team from 'Criminal Minds'. It has some really interesting character dynamics. For example, Dean Winchester's no - nonsense attitude clashes and then meshes with Hotch's leadership style. It also has a great mystery to solve that involves both the supernatural and serial killers.
Maybe in the fanfiction, a member of the CSI team has a personal connection to a case that the Criminal Minds team is investigating. This could lead to some intense emotional moments and also some friction between the two teams as they try to balance the need for objectivity with the personal investment. The story could explore how they overcome these challenges and solve the mystery behind the crimes.
One idea could be that the Scooby Gang from Buffy teams up with the BAU from Criminal Minds to solve a series of murders that seem to have a supernatural and a psychological aspect. Maybe the murders are being committed by a demon that is using human psychological weaknesses to target its victims.