Board Thread:General Discussion/@comment-24145797-20131108221955/@comment-23961350-20131227232709

Or the Astronaut is there with an invincible ship, docking bay, and no monsters, and talking to him/her would allow you to travel back to the overworld (where he/she is in his/her house).

The Lunar boss could be Mars, and drops the Space Dolphin Machine Gun (s.d.m.g, i'm sure you'd all know by now)