Film of nature's most unusual bloodsucker (9)
I believe the answer is:
nosferatu
'bloodsucker' is the definition.
(term for vampire as in the 1922 film Nosferatu)
'film of nature's most unusual' is the wordplay.
'film' becomes 'M' (1931 Fritz Lang film).
'most' means to remove the first letter.
'unusual' is an anagram indicator.
'm'+'of'+'natures'='mofnatures'
'mofnatures' with its first letter taken off is 'ofnatures'.
'ofnatures' with letters rearranged gives 'NOSFERATU'.
(Other definitions for nosferatu that I've seen before include "horror film" , "1922 Dracula film" , "F.W. Murnau's early Dracula film" , "Old film" .)