Complex sentence: Harry reveals he is still alive and duels with Voldemort throughout the castle, as a defiant Neville draws the Sword of Gryffindor from the Sorting Hat and decapitates Nagini, leaving Voldemort mortal.
Split into simpler sentences: Harry reveals he is still alive and duels with Voldemort throughout the castl. Everyone starts to duel each other as a defiant Neville draws the Sword of Gryffindor from the Sorting Hat and decapitates Nagini, leaving Voldemort mortal.