Strange, mysterious (7)
I believe the answer is:
uncanny
This clue is a double definition.
'strange' is the first definition.
(I've seen this before)
'mysterious' is the second definition.
(I've seen this before)
(Other definitions for uncanny that I've seen before include "Seemingly inexplicable" , "Weird - strange" , "Extraordinary, beyond what is normal" , "Strange, mysterious" , "Weird, unearthly" .)