Cutscenes - Get all 99 Tri-Wizard Shields to unlock the cutscenes.
Defeating Fire Salamanders - Hit the Fire Salamanders with Confundus (A). After you get the Aqua spell you can hit them with that and it will kill them immediately.
Defeating Voldemort - Make every attack hit in 3-D mode and avoid his attacks, as they do a lot of damage.
Movie photo gallery - Get all 74 Collector Cards to unlock the movie photo gallery.