Fellow with twitch - alternatively, English monster (9)
I believe the answer is:
manticore
'monster' is the definition.
(manticore is a kind of monster)
'fellow with twitch alternatively english' is the wordplay.
'fellow with' becomes 'man' (I've seen this in other clues).
'twitch' becomes 'tic' (tic is a kind of twitch).
'alternatively' becomes 'or'.
'english' becomes 'e' (abbreviation).
'man'+'tic'+'or'+'e'='MANTICORE'
(Other definitions for manticore that I've seen before include "Mythical stinging beast" , "Fabulous animal" .)