Mysterious magician let out (11)
I believe the answer is:
enigmatical
'mysterious' is the definition.
(I've seen this before)
'magician let out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'magician'+'let'='magicianlet'
'magicianlet' is an anagram of 'ENIGMATICAL'.
(Other definitions for enigmatical that I've seen before include "Puzzling" , "Mysterious" , "about puzzles" .)