Mysterious comic - ace timing (9)
I believe the answer is:
enigmatic
'mysterious' is the definition.
(I've seen this before)
'comic ace timing' is the wordplay.
'comic' indicates an anagram.
'ace'+'timing'='acetiming'
'acetiming' anagrammed gives 'ENIGMATIC'.
(Other definitions for enigmatic that I've seen before include "with a mystery ingredient" , "Like a puzzle" , "Difficult to interpret" , "Cryptic, mysterious" , "not obvious" .)