Spooky, sinister (6)
I believe the answer is:
creepy
This clue is a double definition.
'spooky' is the first definition.
(I've seen this before)
'sinister' is the second definition.
(I've seen this before)
(Other definitions for creepy that I've seen before include "Mysterious" , "Spooky" , "Scary, eery" , "Disturbing, crawly" , "Eerie; repellent" .)