Mental state at the crack of doom? (4)
I believe the answer is:
mood
'mental state' is the definition.
(I've seen this in another clue)
'the crack of doom?' is the wordplay.
'the crack of' is an anagram indicator (I've seen 'cracks' mean this).
'doom' anagrammed gives 'MOOD'.
'at' acts as a link.
(Other definitions for mood that I've seen before include "sullenness may be indicative" , "Feeling of doom" , "feelings" , "Doom (anag)" , "Humour - bad temper" .)