Most jolly times involved embracing sin (8)
I believe the answer is:
merriest
'most jolly' is the definition.
('merry' can be a synonym of 'jolly')
'times involved embracing sin' is the wordplay.
'involved' is an anagram indicator (involved can mean confusing or complex).
'embracing' means one lot of letters goes inside another.
'sin' becomes 'err' (to sin is to err morally).
'times' anagrammed gives 'miest'.
'miest' enclosing 'err' is 'MERRIEST'.
(Other definitions for merriest that I've seen before include "most tipsy" , "Jolliest" , "Most mirthful" , "higher than the rest" , "Gayest, most jolly" .)