Complex sentence: While the entire Zin Empire watches, Zinyak and the Boss battle each other, and with help from the Saints, the Boss kills Zinyak by tearing his head off and emerges victorious.
Split into simpler sentences: While the entire Zin Empire watches, Zinyak and the Boss battle each other. With help from the Saints, the Boss kills Zinyak by tearing his head off and emerges victorious.