Complex sentence: Goku and Vegeta were forced to fuse into Gogeta, who puts up more than a fair fight, and defeats Janemba, and is restored back to the little ogre boy who's body was taken over by him.
Split into simpler sentences: Goku and Vegeta were forced to fuse into Gogeta, who defeats Janemba. Upon defeat, Janemba is restored back to the little ogre boy whose body was taken over by him.