Took off dressed like Batman, about to leave (4)
I believe the answer is:
aped
'took off' is the definition.
(I've seen this before)
'dressed like batman about to leave' is the wordplay.
'dressed like batman' becomes 'caped' (I've seen this in another clue).
'about' becomes 'c' (circa).
'to leave' is a deletion indicator.
'caped' with 'c' removed is 'APED'.
(Other definitions for aped that I've seen before include "was imitative" , "Imitated, mimicked" , "Caricatured" , "Imitated like monkey" , "Followed" .)