Wordnet 3.0
NOUN (1)
1. 
 a particularly baffling problem that is said to have a correct solution; 
- Example: "he loved to solve chessmate puzzles"- Example: "that's a real puzzler"[syn: puzzle, puzzler, mystifier, teaser]
WordNet (r) 3.0 (2006):
mystifier
    n 1: a particularly baffling problem that is said to have a
         correct solution; "he loved to solve chessmate puzzles";
         "that's a real puzzler" [syn: puzzle, puzzler,
         mystifier, teaser]