I think Snape would be the most interesting. His complex past and his hidden loyalties could be fully exposed. We might finally understand all his real intentions and his true feelings towards Harry and his mother.
Probably Draco Malfoy. He's always been a bit of an enigma. With the truth serum, we'd get to know if his mean - spirited actions were all his own or if he was pressured by his family. He might also reveal any hidden admiration he has for the trio or any remorse for his actions throughout the series.
In such a fanfic, characters might reveal long - hidden secrets. For example, Harry could disclose his true feelings about some of his classmates or teachers that he had been suppressing. Maybe Ron would admit his insecurities about always being in Harry's shadow.
Well, in the 'Harry Potter under truth serum' fanfiction, it's likely that we'd see a lot of confessions. Harry could potentially reveal his innermost fears about Voldemort and his own destiny. Teachers like Snape might spill the beans on their past relationships or grudges. It would be a great opportunity for the author to explore the unspoken thoughts and emotions of the characters in a very direct way.
In some 'Harry Potter truth serum fanfiction', there could be a plot where the truth serum is used by students to play pranks on each other at Hogwarts. But these pranks could quickly turn serious as secrets are spilled that were meant to be kept hidden. This could lead to a rift between friends until they figure out a way to fix the situation.
Harry Potter himself is often a central character. The truth serum might be used on him, or he could be the one trying to find out the truth from others. Hermione Granger is also common, as her intelligence might be used to either create or counteract the effects of the truth serum.
One possible fanfiction could be where Hermione accidentally drinks the truth serum during a potions class experiment gone wrong. She starts revealing all sorts of secrets, like her true feelings about Ron and Harry, and also some hidden knowledge she has about Hogwarts' secrets. This could lead to a series of comical and yet somewhat tense situations as her friends try to keep her from saying too much.
An interesting idea could be that Hermione is given the truth serum during a wizarding trial. She has to testify, and the truth serum forces her to reveal some long - held secrets about the Ministry of Magic's inner workings that they were trying to keep hidden. This would create a huge stir in the wizarding world and put Hermione in a dangerous position as she uncovers corruption.
I think it would be really interesting to focus on Hermione. Her thirst for knowledge would make her eager to learn about the world of Eragon, especially the dragon - riding and the different types of magic. She could also bring her logical thinking and problem - solving skills to the table, which would be very useful in both worlds.
It would probably be Harry Potter himself. He's from a world full of magic and mystery, and seeing him interact with the very real and regal world of the Queen would be fascinating.
Pairing Supergirl with Severus Snape could create a really dynamic relationship. Snape has his own dark past and complex personality. Supergirl could potentially see the good in him and try to bring it out. They could have a bit of a clash at first, with Snape being suspicious of her, but over time, they could develop an unlikely friendship or at least a mutual respect as they face common enemies in the wizarding world.