Mystery Quest (or "Hao-kun no Fusihigina Tabi" lit: Hao's Mystery Adventure) follows a young apprentice wizard named Hao as he passes over a series of overworld and castle levels to track down a series of magical artifacts.
It plays very similarly to Super Mario Bros., sharing its side-scrolling presentation and many of its power-ups, such as stars and flowers. It also has a touch of Zelda, as each level is split up with a maze-like castle full of monsters and bosses and a precious item that allows Hao to progress further in the game.
This would be one of only two games developed by Carry Soft for the Famicom/NES, as they normally produced games for Japanese home computers. The company went under a year later.
The US release, "Mystery Quest", was unchanged aside from a few sound effects and the removal of the latter third of the game. Instead of six worlds (including six castles), there are only four.