Soften mood (6)
I believe the answer is:
temper
I believe this clue is a double definition.
'soften' is the first definition.
(I've seen this before)
'mood' is the second definition.
(temper is one's mood or state of mind)
(Other definitions for temper that I've seen before include "Lose it and lose control" , "Mood, maybe angry" , "Volatile anger - don't lose it" , "Adjust" , "Tantrum" .)