Returned mutt with odd flaw that's bitten you? Terrible! (3-5)
I believe the answer is:
god-awful
'terrible' is the definition.
Both the definition and answer are adjectives.
Maybe they are linked in a way I don't understand?
'returned mutt with odd flaw that's bitten you?' is the wordplay.
'returned mutt with' becomes 'god' (I can't explain this - if you can you should give a lot more credence to this answer).
'odd' indicates an anagram.
'that's bitten' is an insertion indicator (some letters bite into others).
'flaw' with letters rearranged gives 'awfl'.
'awfl' enclosing 'u' is 'awful'.
'god'+'awful'='GOD-AWFUL'
Can you help me to learn more?
(Other definitions for god-awful that I've seen before include "Appalling" , "Very unpleasant" .)