Wonder Boy III: The Dragon’s Trap, called Monster World II: Dragon no Wana (モンスターワールドII ドラゴンの罠) in Japan, is a direct sequel to Wonder Boy in Monster Land, and was developed by Westone and published by Sega for the Sega Master System in 1989.
The game should not be confused with Wonder Boy III: Monster Lair, which despite being made by the same people and carrying a similar title, focuses more on being a side-scrolling shoot-’em-up with platform segments.