Sega and Westone's Wonder Boy series was really strange when it came to naming conventions. Wonder Boy started visiting Monster Land and Monster World, and before you know it, Sega put out a Genesis game with the unwieldy Japanese title of Wonder Boy 5: Monster World 3. (For a good overview of the confusing series, I highly recommend Hardcore Gaming 101.)
My point in explaining this is that the last game in the Wonder Boy series was the more-concisely-titled Monster World IV, a game which was supposedly excellent but never made it out of Japan. Almost a year ago, Sega announced that they were bringing a localized version of Monster World IV to XBLA and Virtual Console, but we haven't heard anything since then.
What luck, then, that XBLA Fans have spotted an Xbox Live Marketplace listing for Sega Vintage Collection: Monster World. The bundle will include Wonder Boy in Monster Land, Wonder Boy in Monster World, and the newly-localizedMonster World IV. The listing, since removed, gave a release date of April 25, 2012, though it could be a placeholder date. There's no explanation of why Wonder Boy III: The Dragon's Trap, which is essentially "Monster World 2," is not included. Maybe it's because it's missing any mention of monsters in its English title.