A possible plot is that Ghost Rider's bike gets an upgrade in the DC universe. Maybe it absorbs some of the advanced technology there. He then teams up with the Flash. The Flash is intrigued by the Ghost Rider's speed which is powered by something other than the Speed Force. Together, they race against time to stop a group of villains who are using a time - traveling device to rewrite history. The contrast between the Flash's light - heartedness and Ghost Rider's brooding nature would make for an interesting dynamic.
One idea could be that Ghost Rider somehow gets transported to the DC universe during a magical mishap. He teams up with Constantine to battle a demon that's threatening both the DC world and his own. Another plot could involve Ghost Rider's hellfire having an unexpected reaction with Kryptonite, creating a new type of weapon against Superman's enemies. Or perhaps he meets Raven and they combine their dark powers to fight an ancient evil that neither could defeat alone.
One idea could be a crossover with another Kamen Rider series. For example, Kamen Rider Orga could team up with Kamen Rider Decade. They could travel through different Rider worlds together, facing challenges unique to each world. Another plot could involve a crossover with a popular anime. Maybe Orga has to enter the world of Naruto and fight alongside the ninjas against a common enemy. Or perhaps a crossover with a superhero universe, like the Marvel Universe, where Orga has to join forces with the Avengers to stop an inter - dimensional threat.
A possible plot is that the Ghost Rider's hellfire has an unexpected effect on the vampires in Twilight. Since vampires are undead, the hellfire might either have no effect, or it could be the one thing that can truly destroy them. This could lead to a race between the vampires and the werewolves to either use or stop the Ghost Rider. Also, the Ghost Rider could form an alliance with the werewolves as they are more in tune with the natural order which the Ghost Rider also represents in a way.
A crossover with Kamen Rider Zi - O could also be really cool. Zi - O travels through time, so he could accidentally disrupt the timeline in a way that affects Ghost's world. Ghost might have to team up with Zi - O to fix the timeline while also dealing with the enemies that are taking advantage of the time - chaos. They could encounter different versions of themselves from alternate timelines and have to figure out how to make things right.
Maybe the Ghost Rider's powers are somehow connected to an ancient magic in Equestria. He could be on a quest to find out the origin of his powers and in the process, he befriends Rainbow Dash. Rainbow Dash is intrigued by his ability to fly on his flaming motorcycle and they start to explore different parts of Equestria together, all while uncovering secrets about his powers.
One idea could be that Ghost Rider's powers are somehow needed to stop a demonic threat in the Young Justice universe. Maybe a powerful demon is causing chaos and the team realizes they need the unique abilities of Ghost Rider to send it back to hell. Another plot could involve a member of Young Justice being possessed and Ghost Rider having to help exorcise the demon while also teaching the team about the darker, supernatural side of their world.
Another concept is that Naruto is possessed by a spirit similar to the Ghost Rider. His friends initially fear him, but he has to prove that he can use this new power for good. He might have to learn how to use the power without being consumed by the rage and darkness that often comes with it.
In a fanfiction, the Ghost Rider could form an alliance with Batman. Batman would be intrigued by the supernatural element that Ghost Rider brings. They could team up to take on villains who are using magic or other dark forces. Ghost Rider's powers of hellfire and his unearthly strength would be a great asset to the Dark Knight's strategic mind.
In a fanfiction crossover, Ghost Rider could end up in the Mystery Machine by accident. His flaming skull would surely freak out the gang. However, he might need their help to track down a villain who has escaped into the world that Scooby Doo and his friends inhabit. They could combine their skills, with Ghost Rider's supernatural powers and the gang's mystery - solving abilities.
Another interesting story could be a crossover with 'One Piece'. Ghost Rider could end up on the Grand Line and join the Straw Hat Pirates. His powers could help them in their adventures, especially against powerful foes like the Yonko. He could also have some interesting interactions with Luffy and the crew due to his dark and serious nature.
One idea could be a crossover with Doctor Strange. Ghost Rider's hellish powers could clash or collaborate with Strange's magic in the fight against some interdimensional threats. For example, they might have to deal with demons that are breaking through from different realms.