Complex sentence: Hayden enters the suit, and slaughters his way through infected and non-infected alike, finally finding and killing Nemesis, learning that it was actually Nadia all along.
Split into simpler sentences: Hayden enters the suit, and slaughters his way through infected and non-infected alike, finally finding Nemesis in the process. In the final showdown, Hayden kills Nemesis, learning that it was actually Nadia all along.