I'm not sure if this is allowed here. The game isn't finished but there is a fairly large demo you can play. This game is like Cave Story with a sense of humor.
Update: official site has changed, but the game is still unfinished. New download here:
The Underside Preview (zip) (http://www.superfundungeonrun.com/insignificantstudios/theundersidepreview3.zip)
(http://i708.photobucket.com/albums/ww84/ChaosWolf159/TUSS.png)
Developer's blog and website (http://www.superfundungeonrun.com/)
[mod]old site abandoned; updated post with current links[/mod]