A popular one is 'Crossing Paths'. This fanfiction has an interesting take on the crossover. It starts with a mystery that involves both the Supernatural and Buffy universes. The author does a great job of writing the characters true to their original personalities. Buffy's determination and the Winchesters' tough - guy attitudes are on full display, and the story builds up to a very satisfying climax.
I really liked 'When Hunters Meet Slayers'. It's a well - written fanfic that does a good job of melding the two universes. It has some great action scenes where Sam uses his research skills to help Buffy and her gang figure out a new type of demon that has emerged, which is a combination of a demon from 'Supernatural' and one from 'Buffy'.
One great Buffy and Charmed crossover fanfiction is 'The Power of Two Worlds'. It combines the unique magic systems of both shows in an interesting way. The characters from Buffy and Charmed have to team up to fight a common enemy that threatens both their universes. The author does a good job of keeping the personalities of the original characters intact.
I like 'Buffy in the SGC'. In this fanfic, Buffy is somehow transported to the Stargate Command. The author does a good job of showing how Buffy's slayer skills are both useful and a bit out of place in the military - science - fiction setting of Stargate. There are some really cool fight scenes against Goa'uld with Buffy leading the charge.
One popular 'Supernatural' and 'Buffy' crossover fanfic is 'The Hunter and the Slayer'. It has an interesting plot where Sam and Dean Winchester meet Buffy and her gang. The story is full of action as they team up to fight a common supernatural threat.
One great Merlin - Supernatural crossover fanfic is 'The Hunter and the Warlock'. It combines the magic of Merlin's world with the demon - hunting aspect of Supernatural in a really interesting way. The characters from both shows interact in a believable manner, making for an exciting read.
I really like 'Crossroads of Krypton and the Hunting Life'. In this fanfiction, the writers did an amazing job of bringing in the mythology of Smallville and Supernatural. Dean and Sam Winchester end up in Smallville and get involved with Clark's world. It's full of action and some really cool character moments. It shows how the different powers and skills of the characters from both shows can work together or clash in interesting situations.
One great Supernatural and NCIS crossover fanfiction is 'The Hunt in Quantico'. It combines the mystery-solving aspect of NCIS with the supernatural elements of Supernatural really well. The characters from both shows interact in a very believable way, and the plot keeps you on the edge of your seat.
One great 'Supernatural' and 'Arrow' crossover fanfiction is 'The Hunt in Starling City'. It combines the dark, supernatural elements of 'Supernatural' with the gritty, urban setting of 'Arrow'. The story has Dean and Sam Winchester arriving in Starling City to hunt a demon that's been causing chaos in the criminal underworld, which draws the attention of Oliver Queen and his team. They initially clash but then realize they need to work together to stop the greater evil.
Well, there's 'Parallel Encounters'. In this fanfic, the settings of Supernatural and Tramiplier are merged in a really interesting way. It starts with a character from Tramiplier accidentally stumbling into the world of Supernatural. The story then unfolds as they try to find their way back while getting involved in the ongoing battles against demons and other evils in the Supernatural realm. It's full of action and some really cool character interactions.
A good blend of the two universes' mythologies. In a Buffy Supernatural crossover, it's important to merge the different supernatural elements in a way that makes sense. This could be how the vampires in Buffy's world compare to the demons in Supernatural, or how the magic works in both. It should feel like a natural combination, not just thrown together randomly. The plot also needs to be engaging. It should have a clear goal or mystery that draws the reader in and keeps them interested throughout the story. Maybe it's a new threat that only the combined forces of Buffy and the Winchesters can face.