Answer: enigmatic

AnswerCrossword Clue
ENIGMATICLike Mona Lisa's smile.
enigmaticresembling an enigma; perplexing; mysterious
enigmaticpuzzling, mysterious also ENIGMATICAL
ENIGMATICTough to figure out
ENIGMATICTough to crack
ENIGMATICPerplexing
ENIGMATICHard to figure out.
ENIGMATICSphinxian.
ENIGMATICPerplexing.
ENIGMATICCryptic
ENIGMATICInexplicable.
ENIGMATICPuzzling.
ENIGMATICPuzzling
ENIGMATICVery strange
ENIGMATICBaffling
ENIGMATICMysterious
ENIGMATICHard to figure out
ENIGMATICHard to read