Some controller seen as a monster? (5)
I believe the answer is:
troll
'a monster?' is the definition.
(I know that troll is a type of mythical creature)
'some controller seen' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'TROLL' is hidden in the letters of 'controller seen'.
'as' acts as a link.
(Other definitions for troll that I've seen before include "Dwarf (or giant) of Norse myth" , "Provocative poster" , "ugly cave-dweller" , "Dwarfish creature" , "Fairytale monster" .)