puzzler
From Longman Dictionary of Contemporary Englishpuzzlerpuz‧zler /ˈpʌzlə $ -ər/ noun [countable] informalMYSTERIOUS something that is difficult to understand or explainExamples from the Corpuspuzzler• A bit of a puzzler, for humans.• It is an arcade puzzler game that tests your ability to think fast and move quickly.