In Times, sum up villain (5)
I believe the answer is:
baddy
'villain' is the definition.
(bad guy in a story)
'in times sum up' is the wordplay.
'in' indicates putting letters inside.
'times' becomes 'by' (both can mean 'multiplied by').
'sum up' becomes 'add' (synonyms).
'by' enclosing 'add' is 'BADDY'.
(Other definitions for baddy that I've seen before include "illain" , "Villain in book or film" .)