Well, perhaps in the fanfiction, the Cullens come across the Ghost Rider. Edward, with his mind - reading ability, is unable to understand the Ghost Rider's thoughts as he is something beyond normal vampires' comprehension. Bella, being the center of so much in the Twilight series, could be drawn to the Ghost Rider's sense of justice and power. This might create a love triangle - like situation, but not in the traditional sense, as the Ghost Rider's motives are more about justice and vengeance rather than love. It could add a whole new layer of drama to the Twilight world.
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 the Ghost Adventures crew goes to Forks to investigate some strange paranormal activities that seem related to the vampires and werewolves in Twilight. Maybe they find out that some of the 'hauntings' are actually caused by the territorial disputes between the two supernatural groups.
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.
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 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.
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 interesting plot idea could be Chalice crossing over with another Kamen Rider series, like Kamen Rider Decade. They could team up to fight a common enemy that has the ability to travel across different Rider worlds. Maybe this enemy is stealing the powers of various Riders, and Chalice and Decade have to figure out how to stop it while also learning about each other's abilities and fighting styles.
A really cool plot could involve Kamen Rider Mach crossing over with a time - traveling hero. They have to go back in time to stop an evil organization from changing history in a way that would be disastrous for the future. There could be lots of cool chase scenes and battles in different historical eras.
One idea could be a crossover with another Kamen Rider series like Kamen Rider W. The two Riders could team up to fight a new, powerful villain that is causing chaos across both of their worlds. They would combine their unique abilities and gadgets to take on the enemy.