Fantastic chap turned into strange deity (8)
I believe the answer is:
dynamite
'fantastic' is the definition.
(I've seen this before)
'chap turned into strange deity' is the wordplay.
'chap' becomes 'man' (chap can mean a man).
'turned' shows that the letters should be reversed in order.
'into' indicates putting letters inside.
'strange' is an anagram indicator.
'man' written backwards gives 'nam'.
'deity' with letters rearranged gives 'dyite'.
'nam' placed inside 'dyite' is 'DYNAMITE'.
(Other definitions for dynamite that I've seen before include "Fantastic" , "A1" , "an exciting thing" , "Powerful explosive" , "Explosive - amazing thing" .)