Shurangama even mentioned of so called 'immortal'.
http://online.sfsu.edu/~rone/Buddhism/Shurangama/ps.ss.02.v7.020526.screen.pdf
“Furthermore, Ananda, there are people who do not rely on proper
enlightenment to cultivate samadhi, but cultivate in some special
way that is based on their false thinking. Holding to the idea of
perpetuating their physical bodies, they roam in the mountains and
forests in places people do not go and become ten kinds of
immortals.
“Ananda, some
living beings with unflagging resolution make themselves strong
with doses of medicine. When they have perfected this method of
ingestion, they are known as earth-traveling
immortals.
“Some of these beings with unflagging resolution make themselves
strong through the use of grasses and herbs. When they have
perfected this method of taking herbs, they are known as flying
immortals.
“Some of these
beings with unflagging resolution make themselves strong through
movement and cessation. When they have perfected their breath and
essence, they are known as space-traveling immortals.
“Some beings with
unflagging resolution make themselves strong by using the flow of
saliva. When they have perfected the virtues of this
moisture, they are known as heaven-traveling
immortals.
“Some beings with
unflagging resolution make themselves strong with the essence of
sun and moon. When they have perfected the inhalation of this
purity, they are known as immortals of penetrating
conduct.
“Some beings with unflagging resolution make themselves strong
through mantras and prohibitions. When they have perfected these
spells and dharmas, they are known as immortals with
Way-conduct.
“Some beings with unflagging resolution make themselves strong
through the use of thought-processes. When they have perfected
thought and memory, they are known as immortals with illumining
conduct.
“Some beings with unflagging resolution make themselves strong
through intercourse. When they have perfected the response, they
are known as immortals with essential conduct.
“Some beings with unflagging resolution make themselves strong
through transformations and changes. When they have perfected their
awakening, they are known as immortals of absolute conduct.
“Ananda, these are all people who smelt their minds but do not
cultivate proper enlightenment. They obtain some special principle
of life and can live for thousands or tens of thousands of years.
They retire deep into the mountains or onto islands in the sea and
cut themselves off from the human realm. However, they are still
part of the turning wheel, because they flow and turn according to
their false thinking and do not cultivate samadhi. When their
reward is finished, they must still return and enter the various
destinies.
so perhaps they or ''妖精'' are part of human realm who
practice some unknown ways. and i think immortal does not mean live
forever, maybe live very very long time but still can 'die' by
accident.
/\