The Collaborative International Dictionary of English v.0.48:

Mystify \Mys"ti*fy\, v. t. [imp. & p. p. Mystified; p. pr. &
   vb. n. Mystifying.] [F. mystifier, fr. Gr. ? + L. -ficare
   (in comp.) to make. See 1st Mystery, and -fy.]
   1. To involve in mystery; to make obscure or difficult to
      understand; as, to mystify a passage of Scripture.
      [1913 Webster]

   2. To perplex the mind of; to puzzle; to impose upon the
      credulity of; to baffle; as, to mystify an opponent.
      [1913 Webster]

            He took undue advantage of his credulity and
            mystified him exceedingly.            --Ld.
                                                  Campbell.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mystified
    adj 1: totally perplexed and mixed up; "all this duncical
           nonsense has my brains metagrobolized"- Wall Street
           Journal [syn: metagrobolized, metagrobolised,
           metagrabolized, metagrabolised, mystified]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "mystified":
   addled, at a loss, at a nonplus, at a stand, at a standstill,
   at an impasse, baffled, bamboozled, beat, bewildered, buffaloed,
   confounded, dazed, floored, fuddled, in a dilemma, in suspense,
   licked, muddled, nonplussed, on tenterhooks, perplexed, puzzled,
   stuck, stumped, thrown