Amphibian originally featuring in sci-fi film (3)
I believe the answer is:
eft
'amphibian' is the definition.
(I know that eft is a type of Newt)
'originally featuring in sci-fi film' is the wordplay.
'originally' suggests taking the first letters.
'in' is an insertion indicator.
'sci-fi film' becomes 'et' (E.T. the Extra-Terrestrial).
The initial letter of 'featuring' is 'f'.
'f' placed inside 'et' is 'EFT'.
(Other definitions for eft that I've seen before include "Slimy creature" , "Juvenile newt" , "Little creature" , "Swimmer with feeble legs" , "Pond creature" .)