Complex sentence: With the help of the Legion, Superman X was nearly successful at stopping Imperiex, but he stole the time-travel device and went to the place it was last used for: the 31st century.
Split into simpler sentences: With the help of the Legion, Superman X was nearly successful at stopping Imperiex. However, when he was believed defeated, Imperiex stole the time-travel device and went to the place it was last used for: the 31st century.