The term 'Mysterious Puzzle' can be summed up with the crossword solution of 'ENIGMA' (6 letters). ENIGMA is a type of puzzle that is designed to be difficult to solve. It often involves a code or cipher that must be deciphered in order to find the answer. ENIGMA puzzles have been around for centuries and are still popular today. They are often used as a form of entertainment, but can also be used to test problem-solving skills.