Complex sentence: Cosmi, a three-year old alien, travels to Earth for his mission, in order to impress his father, the Master of Mischief, Cosmi Sr., mostly because Earth is considered the greatest challenge.
Split into simpler sentences: Cosmi, a three-year old alien, travels to Earth for his mission, in order to impress his father, the Master of Mischief, Cosmi. Sr, mostly because Earth is considered the greatest challenge.