Story-related, cannot miss.

Since the last story trophy, the house trophy in the Map Room (whichever house you chose), you’ll have no doubt done a great deal. You’ll have learned to fly, discovered the amazing Room of Requirement, and you’ll have discovered more about the past.

This trophy, and you meeting Charles Rookwood, will pop after you’ve completed the “Percival Rackham’s Trial” main quest - the 20th main mission of the game.