Petrificus Totalus

"Petrificus Totalus - An offensive and effect spell that freezes the target for a few seconds."

Location
Petrificus Totalus Spellbook is located inside the Astronomy Tower that can be accessed by either a broom or through Astronomy Classroom on Floor 2. Note that the Astronomy Classroom and Tower are separated by a spider web, so you need Diffindo to cut get inside the tower.