Mysterious, puzzling (9)
I believe the answer is:
enigmatic
I believe this is a double definition.
'mysterious' is the first definition.
(I've seen this before)
'puzzling' is the second definition.
(I know that puzzling can be written as enigmatic)
(Other definitions for enigmatic that I've seen before include "with a mystery ingredient" , "Like a puzzle" , "with mysterious substance" , "Ambiguous or puzzling" , "Puzzling, like the Sphinx" .)