Harry Potter and the Goblet of Fire
Moody began to beckon students forward in turn and put the Imperius Curse upon them. Harry watched as, one by one, his classmates did the most extraordinary things under its influence. Dean Thomas hopped three times around he room, singing the national anthem. Lavender Brown imitated a squirrel. Neville performed a series of quite astonishing gymnastics he would certainly not have been capable of in his normal state. Not one of them seemed to be able to fight off the curse, and each of them recovered only when Moody had removed it. (15.15)
Hermione suddenly smiled very mischievously, and Harry noticed it too: it was a very different smile for the one he remembered.
"Well ... when I went up to Madam Pomfrey to get them shrunk, she held up a mirror and told me to stop her when they were back to how they normally were [...] And I just ... let her carry on a bit. [...] Mum and Dad won't be too pleased. I've been trying to persuade them to let me shrink them for ages, but they wanted me to carry on with my braces. You know, they're dentists, they just don't think teeth and magic should – look! Pigwidgeon's back!" (23.16-7)
Crouch's principles might've been good in the beginning – I wouldn't know. he rose quickly through the Ministry and he started ordering very harsh measures against Voldemort's supporters. The Aurors were given new powers – powers to kill rather than capture, for instance. And I wasn't the only one who was handed straight to the Dementors without trial. Crouch fought violence with violence, and authorized the use of the Unforgivable Curses against suspects. I would say that he became as ruthless and cruel as many on the Dark Side. (27.151)