Wood nymph is another term for a dryad (tree spirit) in Ancient Greek mythology.
This is the second episode in the series in which Samantha travels back in time (she also did so in What Every Young Man Should Know (1966) ). In both episodes, Samantha requires her mother's assistance in traveling back in time. This is one of several indicators that suggest that Endora is a more powerful witch than Samantha.
In 1958, Michael Ansara (Rufus the Red) married Barbara Eden, who is best known for starring in the rival show I Dream of Jeannie (1965).
Endora reveals that witches (at least a witch like Samantha) are incapable of using their magic when time traveling to the past. This revelation contradicts Samantha's only previous time travel experience, when she re-visited her memories of her and Darrin's courtship in What Every Young Man Should Know (1966). In that episode she used her magic frequently while in the past. While it is possible that a witch could use magic when re-visiting her own memories and experience, but not when traveling to a time and place she had not been to before, the discrepancy is not explained. In both episodes, Samantha requires her mother's assistance to travel through time.