In Greek mythology, Nyx was the primordial goddess of the night, existing since the beginning of creation. While not stated to be of evil nature, many of her children did display more negative aspects, including dominion over blame, deception and death, to name a few. Little of this history seems to have been taken into account by the Castlevania series, however, and she is now depicted as a demonic nurse. Her resistance to the Holy attribute and her item drop, the Princess Coat, may be reference to her more glamorous origins.
The Nyx of Greek myth was also the mother of Thanatos, the Greek personification of Death. However, it is unknown if she has any relation to Death in the series, other than both being servants of Dracula.
As a nurse, Nyx carries a huge syringe and attacks via lunging at the player and striking them with its needle. If struck, the victim, in addition to suffering at the very least twice as much damage as they would have by touching the Nyx herself, will be poisoned. She also speaks in a manner one would expect of a nurse, saying things like: "Medicine Time" (before attacking) and "Don't you feel better now?" (after hitting the player with her poison syringe). One can try to outrun the Nyx while she does this, but it will take some boots well suited for speed or the aid of magic before any attempts can be successful.
They are resistant to the Holy attribute. However, due to their relatively small amounts of HP, they can be dispatched even with Holy-based weaponry with just a few hits. Nyxes can appear either alone or in large groups. If the latter is the case, a single cast of Holy Lightning (even if it's also Holy-based) will usually take care of the whole crowd.
- In the Portrait of Ruin female enemies' illustration, one may notice that Nyx's nurse's hat displays a cross on it, nothing rare given it's the cap of a nurse. However, under close inspection one will also notice it is in fact an inverted black cross, a symbol commonly associated with satanism, again, nothing rare being that Nyx is a demoness.
- This enemy bears an uncanny resemblance to the Yu-Gi-Oh! monster, Injection Fairy Lily, which could be intentional given the amounts of Yu-Gi-Oh! cards that have given a nod to the Castlevania series, not to mention both franchises are from Konami.
- Her use of a syringe that poisons may be an allusion to nurses (and doctors) who intentionally poison their patients, commonly referred to as "Angels of Mercy" or "Angels of Death". However, her ability to inflict poison may be related to her nature as a demonic nurse. Since nurses are associated with healing, it makes sense that a demonic nurse would do the opposite: instead of curing the sick, she causes one to become sick (via poison).