I didn't think defeating Malistaire was magical, I thought of it more as bitter and sad as Sylvia took her defeated husband away but that's just my opinion. I think the most magical moments are in Wizard City so maybe visiting all the profesors or gaining access to Unicorn way? Or maybe it's when you defeat your first boss Rattlebones? Sarai Thunderstrider Magus
My most magical experience, I would have to say is, um, my first day ever on Wizard101, everything was so new and awesome, I didn't think anything was more amazing...