Mystical energy field (4)
I believe the answer is:
aura
'mystical energy field' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for aura that I've seen before include "Particular ambience" , "Perception of distinctive personality" , "Distinct but intangible quality about a person" , "Mystic air" , "Distinctive but intangible quality surrounding a person" .)