That time Nearly Headless Nick caused a commotion to distract Filch
‘‘‘Harry! Harry! Did it work?’ Nearly Headless Nick came gliding out of a classroom. Behind him, Harry could see the wreckage of a large black and gold cabinet which appeared to have been dropped from a great height. ‘I persuaded Peeves to crash it right over Filch’s office,’ said Nick eagerly. ‘Thought it might distract him –’ ‘Was that you?’ said Harry gratefully. ‘Yeah, it worked, I didn’t even get detention. Thanks, Nick!’’
That time Moaning Myrtle revealed the entrance to the Chamber of Secrets…
‘…They said something funny. A different language, I think it must have been. Anyway, what really got me was that it was a boy speaking. So I unlocked the door, to tell him to go and use his own toilet, and then –’ Myrtle swelled importantly, her face shining, ‘I died.’ ‘How?’ said Harry. ‘No idea,’ said Myrtle in hushed tones. ‘I just remember seeing a pair of great big yellow eyes. My whole body sort of seized up, and then I was floating away ...’ She looked dreamily at Harry. ‘And then I came back again. I was determined to haunt Olive Hornby, you see. Oh, she was sorry she’d ever laughed at my glasses.’ ‘Where exactly did you see the eyes?’ said Harry. ‘Somewhere there,’ said Myrtle, pointing vaguely towards the sink in front of her toilet.’
That time Peeves gave Umbridge the farewell from Hogwarts she deserved…
‘Professor Umbridge left Hogwarts the day before the end of term. It seemed she had crept out of the hospital wing during dinnertime, evidently hoping to depart undetected, but unfortunately for her, she met Peeves on the way, who seized his last chance to do as Fred had instructed, and chased her gleefully from the premises whacking her alternately with a walking stick and a sock full of chalk. Many students ran out into the Entrance Hall to watch her running away down the path and the Heads of Houses tried only half-heartedly to restrain them. Indeed, Professor McGonagall sank back into her chair at the staff table after a few feeble remonstrances and was clearly heard to express a regret that she could not run cheering after Umbridge herself, because Peeves had borrowed her walking stick.’
That time the Grey Lady helped Harry work out the location of Ravenclaw’s lost diadem…
"‘And ... and the diadem?’ ‘It remained where I had hidden it when I heard the Baron blundering through the forest towards me. Concealed inside a hollow tree.’ ‘A hollow tree?’ repeated Harry. ‘What tree? Where was this?’ ‘A forest in Albania. A lonely place I thought was far beyond my mother’s reach.’ ‘Albania,’ repeated Harry. Sense was emerging miraculously from confusion, and now he understood why she was telling him what she had denied Dumbledore and Flitwick. ‘You’ve already told someone this story, haven’t you? Another student?’ She closed her eyes and nodded. ‘I had ... no idea ... he was ... flattering. He seemed to ... to understand ... to sympathise ...’ Yes, Harry thought, Tom Riddle would certainly have under- stood Helena Ravenclaw’s desire to possess fabulous objects to which she had little right. ‘Well, you weren’t the first person Riddle wormed things out of,’ Harry muttered. ‘He could be charming when he wanted ...'"
That time Moaning Myrtle helped the Hogwarts Champions out with their Triwizard clues…
"Oh ... I see ...’ said Myrtle, picking at a spot on her chin in a morose sort of way. ‘Well ... anyway ... I’d try the egg in the water. That’s what Cedric Diggory did.’ ‘Have you been spying on him, too?’ said Harry indignantly. ‘What d’you do, sneak up here in the evenings to watch the Prefects take baths?’ ‘Sometimes,’ said Myrtle, rather slyly, ‘but I’ve never come out to speak to anyone before.’ ‘I’m honoured,’ said Harry darkly. ‘You keep your eyes shut!’ He made sure Myrtle had her glasses well covered before hoisting himself out of the bath, wrapping the towel firmly around himself and going to get the egg. Once he was back in the water, Myrtle peered through her fingers and said, ‘Go on, then ... open it under the water!"
That time Peeves fought for good in the Battle of Hogwarts…
“Harry, Ron and Hermione raised their wands at once, ready to strike, but the duellers were weaving and darting around so much that there was a strong likelihood of hurting one of their own side if they cast curses. Even as they stood braced, looking for the opportunity to act, there came a great ‘wheeeeeeeeeeee!’ and, looking up, Harry saw Peeves zooming over them, dropping Snargaluff pods down on to the Death Eaters, whose heads were suddenly engulfed in wriggling, green tubers like fat worms."