mystifying vs mysterious

mystifying and mysterious both are adjectives.

Word	Noun	Adjective	Verb	Adverb
mystifying	No	Yes	No	No
mysterious	No	Yes	No	No

As adjectives, mystifying and mysterious are synonyms defined as:

Other synonyms of mystifying include cryptic, cryptical, deep, inscrutable.

mystifying (adjective)	mysterious (adjective)
of an obscure nature	having an import not apparent to the senses nor obvious to the intelligence; beyond ordinary understanding
	of an obscure nature