Complex sentence: The disguised Karai, wearing the Shredder's armor, orders the Elite to commit seppuku, but only one does; after a hard fight, the Turtles and Karai are the only ones left standing.
Split into simpler sentences: The disguised Karai, wearing the Shredder's armor, orders the Elite to commit seppuku, but only one does. After an ensuing hard fight, the Turtles and Karai are the only ones left standing.