Monster in video green (4)
I believe the answer is:
ogre
'monster' is the definition.
(fairy tale monster)
'in video green' is the wordplay.
'in' indicates a hidden word.
'OGRE' can be found hidden inside 'video green'.
(Other definitions for ogre that I've seen before include "terrible person" , "Terrifying man" , "Brute" , "One making giant strides" , "Evil giant" .)