Mood alters destiny (4)
I believe the answer is:
doom
'destiny' is the definition.
(I've seen this before)
'mood alters' is the wordplay.
'alters' is an anagram indicator.
'mood' with letters rearranged gives 'DOOM'.
(Other definitions for doom that I've seen before include "Condemn to certain destruction" , "A bad lot" , "In the end" , "Unavoidable ill-fortune" , "Judgement" .)