Getting 100% is purely about game progress and collecting the items & tokens in the game:
* Finishing all the levels with all the crests, students in peril, character tokens and true wizard in each level.
* Exploring Hogwarts to find the rest of the character tokens, students in peril and most importantly, the gold bricks.
* Complete the bonus levels in the bank vault of Diagon Alley.
* Finish the Voldemort bonus level in Knockturn Alley (all 200 gold bricks required!).
What you don't
need to worry about:
* Killing X number of Y (with Z).
* Doing X with character Y.
Here is the achievement checklist.StoryCharacters
Oddly, there is no achievement for getting all of the characters, just for a few odd sets. Remember, in addition to finding a token, you must then also purchase the character
Remember that to get Voldemort requires you to have all 200 gold bricks.CollectiblesActions
The only actions you need to undertake is rescuing all the students in peril & getting True Wizard in all the levels. Others, like the time turner, are awarded in the pursuit of gold bricks.