Complex sentence: He has a large amount of killing intent that he honed from his days as a Chronos member, and as a result he often has sudden mood swings, going from carefree to serious in an instant, especially when Creed is mentioned.
Split into simpler sentences: He has a large amount of killing intent that he honed from his days as a Chronos member. As a result, he often has sudden mood swings, going from carefree to serious in an instant, especially when Creed is mentioned.