I don't know for sure as I haven't read it. It could be original characters created by the fanfiction writer, or it might be based on existing characters from a related story or movie.
I don't know since I haven't read it, but it could be a group of friends who like to play pranks on each other.
Obviously Naruto would be the main character as it's about him being the 'god of pranks'. His friends like Sasuke, Sakura, and Kakashi are likely to be important characters too. Sasuke might be the target of many of Naruto's pranks, which could add some humorous tension between them. And Kakashi, as Naruto's teacher, might be constantly trying to stop Naruto's pranks or get caught up in them.
Typically, Harry is one of the main ones. He has a knack for getting into and out of trouble with his pranks. Hermione might also be involved in some pranks in a more strategic way, using her vast knowledge of magic to create unique and elaborate pranks. And of course, the Weasley twins are almost always at the center of the most elaborate and chaotic pranks in the fanfiction.
Since it's a fanfiction, it could be taking the concept of '28 pranks later' and adding its own unique spin. It might explore the relationships between the characters through the prism of these pranks. For example, some characters could become closer because they plan pranks together, while others might have conflicts due to being the victims of pranks. There could also be a character arc where someone who starts as a prankster learns the value of not causing too much trouble.
Obviously, Percy Jackson himself. He's the one doing the pranking. Then, there would probably be the gods like Zeus, Poseidon, and Athena who are the targets of his pranks. His friends like Annabeth might also be involved, either helping Percy with the pranks or trying to stop him when they think he's going too far.
Obviously Naruto is the main character as he is the one usually pulling the pranks. His friends like Shikamaru might also be involved, either as victims of the pranks or as accomplices. Sakura could be in there too, perhaps getting annoyed at Naruto's pranks or being part of a prank on someone else.
The main character is Naruto for sure. When it comes to the Anbu, there could be some new and original Anbu characters created just for this fanfiction. They could have unique abilities and personalities. Naruto's relationship with these made - up Anbu characters could be really interesting. He might prank them in ways that play off of their individual quirks. For example, if one Anbu is really proud of his speed, Naruto could set up a prank that makes it seem like he's much slower than he thinks.
The Weasley twins, Fred and George, are often the main instigators. They have a reputation for their mischievous pranks in the original series, so it's natural that they would be at the forefront of pranking Umbridge in fanfiction. Their creativity and disregard for authority make them perfect for coming up with elaborate and hilarious pranks against her.
The Weasley twins, Fred and George, are often the main instigators of pranks in Hogwarts fanfiction. They have a natural knack for mischief and are always coming up with new and creative ways to cause chaos in the school. Their products from Weasleys' Wizard Wheezes also play a big role in the pranks they pull.
Obviously, Danny Phantom is one of the main characters as the title implies he's the one doing the pranking. And then, members of the Justice League like Superman, Batman, Wonder Woman, Flash, etc. would be the ones being pranked.