Sam would probably be very protective. She'd be the one making sure Danny was fed and clean. Tucker would be more into trying to figure out how to fix the situation using his tech skills. They'd both be really shocked at first, but then quickly adapt to taking care of Danny. They might have to come up with excuses for Danny's parents about why he wasn't around or why he was acting so strange.
At first, Sam and Tucker would be completely stunned. Sam might be a bit more calm on the surface, but inside she'd be freaking out. Tucker would be panicking and running around in circles. Once they got over the initial shock, Sam would start taking on the role of a caregiver. She'd make sure Danny had proper clothes and a safe place to sleep. Tucker would start researching all the books and data he had on ghosts and strange transformations. They'd have to work together to keep Danny out of harm's way and also try to find a way to reverse his condition.
Sam would probably be really intrigued. She might see it as a cool new form for Danny and would be eager to learn more about how it affects his powers. Tucker, on the other hand, would likely be more concerned about how to reverse it at first. But once he realizes that Danny can still do some cool things as a mermaid, he'd be excited too.
His parents might be really confused at first. They've been hunting ghosts, and suddenly their son is a baby again. They'd probably be worried about his well - being and try to figure out what happened using their scientific knowledge. Jazz, his sister, would likely be very protective. She'd take on a more motherly role, making sure Danny is fed, clean, and safe.
Sam would probably be the first to be curious and excited. She might start researching about any possible connection between ghosts and dragons right away. Tucker would be a bit more cautious at first, but also amazed. He might be worried about how Danny can control this new form and if it will put him in more danger. Jazz would initially be shocked but then would try to be very supportive. She might offer to help Danny figure out the psychological aspects of having this new form and how it affects his identity as a half - ghost.
Well, one possibility could be that Danny gets hit by some sort of ghostly ray that de - ages him. His friends, Sam and Tucker, would then have to take care of him while trying to figure out how to reverse the effect. They might face challenges like hiding him from his parents, who would be really confused if they saw their teenage son turned into a toddler. Also, Danny's ghost powers could be all out of whack in his toddler form, causing some unexpected chaos around town.
Danny would probably be extremely hurt. He might initially go into denial, not wanting to believe that his friends could do such a thing to him. He'd keep trying to reach out to them, hoping it was all a misunderstanding.
Their friends might be really shocked at first. Tucker, for example, might not know how to handle the situation. He could be worried about how it will affect their group dynamic. Jazz might be more understanding and try to offer support, but also be a bit concerned about the practicalities of them being so young. Some of their other friends might be judgmental, thinking they're too young and not ready for this big step.
Danny would probably be heartbroken. He really cares about Sam, so finding out she cheated would be a huge blow. He might go into a state of denial at first, not wanting to believe it.
His personality might become more innocent. As a kid, he's not as cynical as when he was a teen. He might be more open - minded and trusting.
One idea could be that Danny turns into a girl due to a ghostly spell gone wrong. In the fanfiction, he could struggle with the new body while still having to fight ghosts. Maybe his friends don't recognize him at first, leading to some comical and tense situations.
The Joker would probably be both intrigued and excited. He might see Danny's powers as a new and interesting toy to play with. He could try to find ways to manipulate Danny into using his powers for the Joker's own chaotic purposes. For example, he might trick Danny into using his intangibility to break into a high - security building so the Joker can plant some crazy bombs or something.