It could be that Beast Boy is actually undercover as Slade's apprentice. He might be trying to gather information to take Slade down from the inside. This would add an element of mystery to the fanfic. He would have to pretend to be on Slade's side while secretly working against him, which would require a lot of acting skills on Beast Boy's part.
If Beast Boy becomes Slade's apprentice, some of the Titans might try to reach out to him secretly. They would hope to bring him back to the good side. This could create a sub - plot where there are secret meetings and attempts at persuasion. But it would also be very dangerous for those Titans who try, as they could be caught by Slade and put in jeopardy.
Well, he could be rescued by his friends. Maybe Raven uses her magic to track him down and then the team like Cyborg and Starfire fight off the captors.
It's also possible that Nightwing and Slade end up having a long conversation during the captivity. Slade might try to convince Nightwing to join his side, perhaps by appealing to some sense of justice that he thinks Nightwing is missing. Nightwing, of course, would resist, but this could lead to some interesting character development for both of them as they debate their different ideologies.
Well, he could start breathing fire uncontrollably and accidentally set the Titans' tower on fire. Then he'd have to figure out how to put it out while still in dragon form.
Well, in a fanfiction where YJ Robin is kidnapped by Slade, one possibility is that the other members of the Young Justice team would immediately start a rescue mission. They would use their unique skills and powers to track down Slade's hideout. For example, Aqualad might use his connection to the water and sea life to gather intel, while Superboy could use his strength to break through any barriers in their way. Robin himself would likely be using his wits to try and outsmart Slade from within the captivity.
It could be a mad scientist who wants to study Beast Boy in his beast form and keep him caged for experiments.
Well, perhaps it could be about Beast Boy losing control over his powers and fully becoming the beast all the time. Maybe there's a curse or some dark magic at play that forces him into this state.
It could be that the kiss is just the beginning of a long and complicated relationship. They might have misunderstandings at first. For example, Starfire's different way of expressing emotions might confuse Beast Boy. But as time goes on, they learn to communicate better. They could also start to share their dreams and fears with each other. This would make their relationship deeper and more meaningful.
In fanfiction, the relationship between Slade and Beast Boy can be very flexible. Regarding whether Slade knows Beast Boy's demon dark secret, it could go either way. Fanfiction writers often take creative liberties. They might have Slade find out the secret as a way to add drama or a new twist to the story. For example, if Slade knows, he could use it against Beast Boy in a battle of wits or strength. On the other hand, if he doesn't know, the story could be about how Beast Boy tries to keep it from him, adding an element of mystery and tension.
Well, in this fanfic, Beast Boy might show off his unique shape - shifting abilities to the Titans in a really cool way. Maybe he uses his powers to save the day in a new and unexpected scenario.