Nyx is introduced to Riley early in the episode, where Jacks tells him about Riley's vision. He hypothesizes that it had something to do with "limbic resonance" and moves on to talk about a drug called DMT.
Later, in his house, he passes around the drug to Riley's friends. When Riley seems impassive to what they're doing, Nyx coaxes her into getting high by talking about how he pushed everyone away until they tried the drug.
However, Nyx happened to be set up by Jacks and his friend, Nocker. Shots are exchanged, and Nyx manages to kill Jack and his friend, before being shot himself.
Nyx, apparently still alive after their ordeal, ambushes Riley. He demands for his drugs and money back, not believing her when Riley says she threw them away. He drawls about how violence can change the simplest of things and uses a plastic bag to suffocate her. Riley, however, knocks him out and escapes through Will.