One idea could be that the lycans and vampires in the Underworld are being haunted by some strange demonic presence. The Ghost Rider, sensing this unholy chaos, rides into their world. He could initially be seen as a threat by both sides but then they realize he's there to fight a common enemy, like a powerful demon that wants to use the eternal war between the lycans and vampires to its advantage. The Ghost Rider's hellfire powers could be a new and terrifying element in the Underworld's dark and violent setting.
I think the Ghost Rider would be the most interesting. His otherworldly powers and his tortured soul make him a very unique character. In the Underworld setting, his hellfire and penance stare would be extremely effective against the vampires and lycans. Also, seeing how he interacts with the different factions in the Underworld, whether he's feared or respected, would be really cool to explore.
There's a Ghost Rider crossover with Blade that's really interesting. In this fanfiction, their shared vampire - hunting nature brings them together. They have different approaches though. Ghost Rider with his hell - based powers and Blade with his vampire - slaying skills make for an exciting dynamic as they face a new breed of vampires that are immune to normal vampire - killing methods.
A good Ghost Rider crossover fanfiction should have a well - developed plot. For example, if it's a crossover with Spider - Man, the story should find a logical reason for these two very different characters to meet. Maybe a new villain is causing chaos in New York and their paths cross while trying to stop it.
In a Ghost Rider - Avengers crossover fanfiction, the story could start with Ghost Rider being drawn into the Avengers' world due to some strange rifts in the dimensions. The Avengers, being the protectors of the Earth, are a bit skeptical of this new, flaming - skulled hero. However, as they face a powerful interdimensional foe that can only be hurt by Ghost Rider's hellfire, they have to team up. Ghost Rider's unique abilities like his superhuman strength and his ability to track down evil could be crucial in the fight. Also, his relationship with the supernatural could open up new storylines for the Avengers who are more used to dealing with earthly threats.
Definitely Constantine. Constantine is a master of the occult in the DC universe, and Ghost Rider has his own connection to the supernatural. Their combined knowledge and powers could lead to some really cool adventures. They could face off against demons and dark magic users that neither could handle alone.
Well, perhaps the Ghost Rider somehow ends up in Konoha. Naruto, who has a natural inclination to befriend the outcast, tries to communicate with him. The Ghost Rider's presence starts to cause chaos as his very nature disrupts the chakra balance in the village. Naruto has to figure out a way to calm the Ghost Rider down. In the process, they discover that there is a common enemy lurking in the shadows, an ancient evil that has been manipulating events in both the Naruto world and the world the Ghost Rider comes from. Together, they embark on a journey to find and defeat this evil, with Naruto using his Rasengan and the Ghost Rider using his Penance Stare.
A powerful dark wizard from the human world who has found a way to cross over into Equestria. He wants to harness the magic of the Elements of Harmony to increase his own power. He sees the Ghost Rider as a threat to his plans and tries to eliminate him while also causing chaos in Equestria.
A fanfiction idea could be that the Powerpuff Girls are accidentally transported to the world where Ghost Rider exists. There, they have to find a way back home while also dealing with the local threats. Ghost Rider could be initially suspicious of these strange, powerful little girls. However, as they prove their good intentions, he decides to help them. The contrast between the colorful, girly world of the Powerpuff Girls and the dark, gritty world of Ghost Rider would make for an interesting setting.
Well, it often starts with a premise that brings the two universes together. Maybe a dimensional rift or some kind of magical - technological event. Then the characters meet. For instance, Ghost Rider might be drawn to the chaos caused by the Transformers' battles on Earth.