Fate altered mood (4)
I believe the answer is:
doom
'fate' is the definition.
(I know that fate can be written as doom)
'altered mood' is the wordplay.
'altered' indicates anagramming the letters.
'mood' with letters rearranged gives 'DOOM'.
(Other definitions for doom that I've seen before include "Disastrous destiny" , "In disaster" , "Sentence" , "Death, destruction" , "Day of reckoning" .)