sudoku vs mystifier

sudoku and mystifier both are nouns.

Word	Noun	Adjective	Verb	Adverb
sudoku	Yes	No	No	No
mystifier	Yes	No	No	No

As nouns, mystifier is a hypernym of sudoku; that is, mystifier is a word with a broader meaning than sudoku:

sudoku: a number puzzle in which the numbers 1 through 9 must be placed into a grid of cells so that each row or column contains only one of each number
mystifier: a particularly baffling problem that is said to have a correct solution

Other hypernyms of sudoku include puzzle, puzzler, teaser.

sudoku (noun)	mystifier (noun)
a number puzzle in which the numbers 1 through 9 must be placed into a grid of cells so that each row or column contains only one of each number	a particularly baffling problem that is said to have a correct solution