Wonder Boy III: Monster Lair, best known in the US and Europe as simply Monster Lair, is the third game in the Wonder Boy series. Monster Lair retains the gameplay of the first Wonder Boy (which also became the basis for Adventure Island), presenting a side-scrolling platformer/brawler in which the player had to continually keep their energy up with food.
Wonder Boy III was originally developed for the Arcades like its forebears, releasing in the November of 1988 in Japan. It later saw a conversion for the PC Engine CD-ROM/TurboGrafx-CD by Alfa System and Hudson, and the Sega Mega Drive (in Japan and Europe only) courtesy of Sega. Both the TurboGrafx-CD and Mega Drive versions of the game were added to the Nintendo Wii's Virtual Console, in 2007 and 2009 respectively.
The game is not to be confused with the other Wonder Boy III, Wonder Boy III: The Dragon's Trap. The Dragon's Trap was an original game for the Sega Master System (and later ported to the Game Gear) and is an open-world game akin to Metroid or Castlevania II: Simon's Quest.
Monster Lair plays like a platformer and shooter. The game stays similar to previous Wonder Boys in that the titular character runs from left to right losing health as time passes. As Wonder Boy loses health he collects fruit in order to regain stamina and progress through the game.
Gameplay diverges from previous Wonder Boys in the shooting sequences. Certain levels will have Wonder Boy riding atop of dragons and other monsters, and the goal is to shoot all enemies on screen. Health in the shooting levels is only lost once hit, rather than continuously, but the player can still collect fruit for health. The shooting levels can best be compared to side-scrolling arcade shooters. All boss encounters are on shooting levels, and the shooting sequences are featured often in the game.