Setter's run in mire and grease, flipping mess! (9)
I believe the answer is:
imbroglio
'mess' is the definition.
(both can mean a mess or confusion)
'setter's run in mire and grease flipping' is the wordplay.
'setter's' becomes 'I'm' (referring to the person who set the crossword).
'run in mire' becomes 'brog' (I can't explain this - if you can you should believe this answer much more).
'and' says to put letters next to each other.
'grease' becomes 'oil' (I've seen this before).
'flipping' shows that the letters should be reversed in order.
'oil' reversed gives 'lio'.
'im'+'brog'+'lio'='IMBROGLIO'
Can you help me to learn more?
(Other definitions for imbroglio that I've seen before include "Intricate and confusing heap or situation" , "Complicated situation" , "Confused and tangled situation" , "quandary" , "massive jam" .)