Part of antihero, guess one's villainous (5)
I believe the answer is:
rogue
'one's villainous' is the definition.
'part of antihero guess' is the wordplay.
'part of' says the answer is hidden in the clue.
'ROGUE' is hidden within 'antihero guess'.
(Other definitions for rogue that I've seen before include "Villain - freak" , "Scallywag" , "Bad person" , "Rascal or reprobate" , "Impish, likeable person" .)