Backing humour in unpleasant fate (4)
I believe the answer is:
doom
'unpleasant fate' is the definition.
(doom is someone's downfall or death)
'backing humour' is the wordplay.
'backing' says the letters should be written backwards.
'humour' becomes 'mood' (I've seen this before).
'mood' backwards is 'DOOM'.
'in' is the link.
(Other definitions for doom that I've seen before include "A bad lot" , "Dire fate" , "Unfortunate fate" , "Inescapable fate" , "Terrible fate; death" .)