They should have seen it coming. Really they should not have been so shocked. I am the son of a Marauder, godson to another child of a Marauder. So it should come as no surprise that I enjoy pranks. Thanks to the nifty genetic inheritance from my mother I am able to get away with them without the use of the invisibility cloak, or the infamous Marauder's map. Though I know I could have the map if I asked James Sirius for it, but I made it without it until he started Hogwarts, and really he needed it more than I did.
I am pretty sure that McGonagall knows who is behind the pranks. But seeing as no one can Identify me for certain, she had no proof. I do know that Professor Longbottom knows, but he would never tell. His loyalty to my Godfather would prevent it unless I did something truly dangerous. While setting a horde of Nifflers loose in the Great Hall, painting the Slytherin common room pink, or slipping canary creams onto the tables at dinner were probably not the best ideas, they weren't dangerous.
I have the perfect alibi for all my pranks. No one can identify me. After all, I never use the same disguise twice. I found the perfect place to store my extra house robes. The Room of Requirements really is quite amazing. Thank you Godfather and Aunt Hermione for telling me about it. I know Aunt Hermione didn't intend for me to use it as such, but it really is a safe place to lie low. Now my "disguises"? Well those are the best part.
You see, thanks to my metamorphmagus abilities, I can easily change my appearance while I do these things. Getting the other house robes was simple when you have an Uncle like George Weasley. I have to send him letters about what pranks I have pulled and work in the joke shop in the summers, but it was totally worth it. Just yesterday, used the Ravenclaw robes to sneak into their common room and charm all their books to appear empty. The panic that ensued as they lost their minds was hilarious. If anyone saw anything, they could only say it was the redheaded, short boy from their house. Upon exiting the common room, I stow my Ravenclaw robes, and switch back my appearance. Nothing to see here. Just a tall, turquoise haired boy from Hufflepuff.
Despite all this, I find myself summoned to the Headmistress office. She offers me ginger biscuits, and tea. She asks me about the Ravenclaw incident, and my whereabouts. But seeing as I have a room to myself (ah the perks of being Head Boy), no one else can possibly verify if I was or was not studying in my dorm. After all, my top of the class marks show I do my work, and all the professors will agree I am polite and studious. While she can't prove I had anything to do with it, I know she suspects. As she dismisses me, she calls out. "Mr. Lupin, you do your father and his friends proud. I was always fond of them. I see alot of his traits in you. Oh and well done on the Slytherin common room. I do believe you managed to out do the Marauders and the Weasley Twins." I smirk, as I walk out the door, "No idea what you are talking about Headmistress."