Fantastic to croon about TV show (8)
I believe the answer is:
smashing
'fantastic' is the definition.
(I've seen this before)
'croon about tv show' is the wordplay.
'croon' becomes 'sing' (I've seen this before).
'about' is an insertion indicator.
'tv show' becomes 'mash' (I've seen this in another clue).
'sing' enclosing 'mash' is 'SMASHING'.
'to' acts as a link.
(Other definitions for smashing that I've seen before include "Breaking things - super!" , "ace" , "Committing act of vandalism" , "Fantastic" , "Excellent; breaking" .)