Little devil in the manner of a beast (6)
I believe the answer is:
impala
'beast' is the definition.
(I've seen this before)
'little devil in the manner of a' is the wordplay.
'little' means to remove the last letter (the word is not quite complete).
'devil' becomes 'imp' (devilish creature).
'in the manner of' becomes 'a la' ('a la' means 'in the manner of', as in 'a la mode').
'imp'+'ala'+'a'='impalaa'
'impalaa' with its final letter taken away is 'IMPALA'.
(Other definitions for impala that I've seen before include "Graceful antelope" , "horned beast" , "graceful African runner" , "prodigious bounder" , "horny type" .)