Fred and George Weasley are very likely candidates. They are known for their love of pranks and their mischievous nature. They might see pranking Dumbledore as the ultimate challenge.
Mario and Luigi are the most likely. They are always looking for ways to outwit Bowser, and pranking him would be a fun way to get back at him for all his evil deeds.
His friends are the most likely ones. They know his habits and routines well enough to pull off some great pranks. For example, if Leo is always punctual, they could set his alarm clock wrong to make him late.
Obviously, Dumbledore himself is the central figure. Then there would be characters like Harry Potter, who might have mixed feelings about Dumbledore after learning some of his secrets. Hermione Granger could also be involved, using her logical mind to analyze the situation. And perhaps members of the wizarding government, such as the Ministry of Magic officials who might be the ones to judge Dumbledore.
In certain 'dumbledore gets pranked fanfiction', a popular prank is to make Dumbledore's office furniture float and move around chaotically. Imagine him trying to sit at his desk and the chair keeps scooting away or the desk starts doing a little dance. Also, there could be a prank where his glasses show false images, like seeing a dragon in the hallway when there's actually just a cat.
Sasuke is a likely target. He's so serious all the time, and Naruto would find it quite fun to break his stoic demeanor with a good prank. Another one would be Sakura. She can be a bit hot - headed, and Naruto's pranks on her could lead to some really comical reactions. And of course, Kakashi. He's always laid - back, but Naruto might want to test his limits with some crazy pranks.
There's also a chance that Dumbledore gets caught by a group of rogue magical creatures. For instance, if he was exploring an area that was supposed to be off - limits to wizards and the creatures there saw him as an intruder. They might not be as rational as wizards and could hold him captive without really understanding who he is.
It could be Severus Snape. He has a complex relationship with Dumbledore. Maybe Snape discovers some of Dumbledore's plans that he doesn't agree with regarding Harry Potter. He then sends a Howler in a fit of anger to express his disapproval.
The Ministry of Magic could be responsible. They might be jealous of Dumbledore's power and popularity. They could see him as a threat to their own authority and come up with some false charges to arrest him. For example, they could claim he was hiding information about a dangerous dark wizard.
For Harry, his friends like Ron and Hermione are likely to be his allies. They've always been by his side through thick and thin in the original series, so it's natural for them to support Harry in a confrontation with Dumbledore. Neville could also be an ally, given his growth and courage shown in the books.
Hermione would be a likely candidate. She is Harry's best friend and is very intelligent. She could use her knowledge of spells and magic to come up with a plan to help Harry escape. For instance, she might create a diversion or find a way to disable the security around Dumbledore's area.