It would be quite odd. If Harry Potter experimented on fanfiction, it could imply that the magic in his world had some sort of connection to the creative realm of fanfiction. Maybe he was trying to understand different interpretations of his own story or the wizarding world. But this would also blur the lines between the official story and the fan - made ones, and it might disrupt the integrity of the original Harry Potter narrative.
Well, one possibility is that in fanfiction, Death Eaters who survived the war might capture Harry Potter and experiment on him to extract the power of his connection to Voldemort. They might believe that this power could be harnessed for their own evil purposes. Also, there could be fanfictions where rogue wizards from other countries experiment on Harry, seeing him as a unique specimen due to his fame and his defeat of the most powerful dark wizard in history.
In 'sonic gets experimented on fanfiction', one possibility is that the experimenters are from an alien race. They might be curious about Sonic's abilities which are far beyond what they've seen in their own world. So they capture him and start running all sorts of tests on him, from physical examinations to tests on his cognitive abilities.
Well, Harry could marry one of the veelas. Given their beauty and allure, it would add an interesting dynamic to the story. Their relationship could involve Harry having to deal with the jealousy of other wizards and also the cultural differences of the veelas. Or he could marry a descendant of one of the founders of Hogwarts. This would tie in a lot of Hogwarts history into their relationship, and their wedding could be a grand event that unites different factions within the wizarding community who have ties to the founders.
Maybe Dumbledore, if he were still alive in the fanfiction. Dumbledore was highly respected and had a great influence. Knighting Harry would be a way for him to publicly recognize Harry's achievements and heroism on a grand scale.
It could be Dr. Eggman. He's always been after Sonic and trying to defeat him. Experimenting on Sonic could be his new way to find Sonic's weaknesses or to gain his powers for himself.
Hermione Granger is a very common character. Since she is Harry's best friend, she would likely be there to help him understand and control his new superpowers. She might research in the library to find out how these powers came about and how to use them effectively. Ron Weasley is also common. He would probably be both in awe and a bit jealous of Harry's new powers at first but would still support him in the end.
It could be Voldemort. He might use hypnosis as a new way to get to Harry, trying to make him a weapon against the Order of the Phoenix. Another possibility is a new dark wizard who wants to make a name for himself by controlling Harry Potter.
It could be Dumbledore. Dumbledore is always full of surprises and he might give Harry the staff as a last - resort weapon to fight against Voldemort. He could have been secretly researching the staff and its powers and decided that Harry was the only one who could wield it properly.
No. Fanfiction that involves such inappropriate and sexual content is not acceptable in the Harry Potter fandom. The Harry Potter series is mainly aimed at a wide range of audiences including children and young adults, and this kind of content goes against the spirit of the original work which is about magic, friendship, and heroism.