Occasionally bestial character in Antigone, perhaps (3)
I believe the answer is:
eta
'character in antigone perhaps' is the definition.
(eta is a Greek letter)
'occasionally bestial' is the wordplay.
'occasionally' indicates alternate letters.
The alternate letters of 'bestial' are 'ETA'.
(Other definitions for eta that I've seen before include "indicating when flight is due" , "character abroad?" , "When you'd expect to see" , "Foreign letter" , "Letter of Greek alphabet" .)