Does Nemesis stop chasing you?
Does Nemesis stop chasing you? If you flee an optional encounter, he will usually follow you through a couple of rooms, but then disappear until the next scripted encounter (when you progressed further in the game). So, no, he won't chase you through the entire game.
Is Nemesis still human?
As with the original, the remake Nemesis also mutates after suffering heavy damage. However the development team chose to give it a more animalistic, quadrupedal body with diminished intelligence, the in-universe reasoning being that the parasite could no longer maintain a humanoid form.