Complex sentence: All of a sudden, Logan notices all the metal around him starting to shake and whirls around to find Magneto, who claims he needs Wolverine's help to combat a threat to all mutants.
Split into simpler sentences: All of a sudden, Logan noticed that all the metal around him were starting to shake. He whirled around to find Magneto, who claimed he needs Logan's help to combat a threat to all mutants.