Complex sentence: The four then band together to fend off the zombie horde once more, finding themselves affected by Element 115; the personalities and memories of their original incarnations begin to bleed into theirs.
Split into simpler sentences: The four then band together to fend off the zombie horde once more. As the fight goes on, the characters find themselves affected by Element 115, and the personalities and memories of their original incarnations begin to bleed into theirs.