Mine is gathering fluff when viewed in the mirror (5,4)
I believe the answer is:
booby trap
'mine' is the definition.
(booby trap is a kind of mine)
'gathering fluff when viewed in the mirror' is the wordplay.
'gathering' becomes 'party' (party is a kind of gathering).
'fluff' becomes 'boob' (both can mean an error).
'when viewed in the mirror' says the letters should be written backwards (letters reflected back).
'party'+'boob'='partyboob'
'partyboob' in reverse letter order is 'BOOBY-TRAP'.
'is' is the link.
(Other definitions for booby trap that I've seen before include "hidden hazard" , "Hazard for the unwary" , "mine?" , "Device for practical joke" , "hidden bomb, perhaps" .)