Revealing mistake: In the scene where Harry and co. are in the Room of Requirement, at several points during this scene, you can tell by the way the light shines that Harry's glasses are missing their lenses, especially in close up shots of Harry.
Revealing mistake: When Lupin is on the castle bridge and reunites with his wife-right after the scene where Neville beckons the dark wizards that disintegrate in the force-field-if you carefully watch the right hand corner of the screen, a very obvious green screen error can be seen in the castle window.
Revealing mistake: When Gregory falls in the fire and dies, while he is falling, you can very obviously tell that it's a stunt double who looks nothing like Josh Herdman.
Answer: It's a little complicated. Voldemort actually died by his own hand, though unintentionally. Voldemort believed he commanded the Elder Wand and cast the Avada Kedavra curse at Harry with it. However, Harry was actually the Elder Wand's master. Because wands are somewhat sentient, the Elder Wand recognized Harry as his master, so the killing curse rebounded off him, and went back to Voldemort, striking him dead. All of Voldemort's Horcruxes had been destroyed, so he was no longer protected by them. At the same time, Harry cast the Expelliarmus charm, causing the Elder Wand to be ejected from Voldemort's hand into his.
raywest ★