Complex sentence: In the film, Megatron successfully kills Optimus Prime and much of the cast of the television series and is reborn as Galvatron, siding with a gigantic, planet-devouring Transformer called Unicron, and the remaining Autobots set out to defeat them.
Split into simpler sentences: In the film, Megatron kills Optimus Prime and much of the cast of the television series and is reborn as Galvatron. He sides with a gigantic, planet-devouring Transformer called Unicron, and the remaining Autobots set out to defeat them.