Complex sentence: He managed to possess three lightsabers (one in each hand and the third using his left foot) to fight Mundi as they fought lightsabers blazing until clone troopers arrived to save the surviving Jedi from Grievous.
Split into simpler sentences: He managed to possess three lightsabers (one in each hand and the third using his left foot) to fight Mundi. As they fought lightsabers blazing, clone troopers arrived to save the surviving Jedi from Grievous.