Fairytale monster (5)
I believe the answer is:
troll
'fairytale monster' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for troll that I've seen before include "Dwarf (or giant) of Norse myth" , "Fish - gnome - sing" , "Internet provocateur" , "Supernatural creature of Scandinavian folklore" , "Legendary Norwegian dwarf (or giant)" .)