You need to unlock all the characters with the little green footprint ability in the spot on the dial where Harry has his cloak.
Sirius Black(Dog): Located in 3-6. Dark Magic is required to unlock a cabinet in the section where you use the purple gargoyle to smash a window to get the potion component.
Professor McGonagle(Cat): Transfiguration Classroom. Requires Reducto to access the classroom. Just complete the transforming spell training and her token will appear.
Peter Pettigrew(Rat): Located in 3-4. Dark Magic is required to unlock a cabinet when you are in the shrieking shack.
Rita Skeeter(Beetle): Slytherin Dorm Entrance. Required Reducto and a strong character. Destroy all the locks on the floor with reducto then use the strong character to pull the two chains in the pools of water on either side of the dorm door entrance.
Remus Lupin(Werewolf): Located in 3-5. Requires Reducto. The token is located in a chest that is to the right of the tree in the middle of the water. Instead of jumping across to the little tree go the the far right and destroy some weeds and the chest will be right there.
I am pretty sure this is all the Animagus characters.
Thanks GeoKetch for pointing out Rita was a beetle and not a spider.