A long time ago I made up rules for a
40K mini game. I would often house group games with players switching opponents after finishing their games. People would finish up their games at different times, so I put out a small table and models for a mini game just to entertain the waiting gamers. The Lurker Terror Scenario became pretty popular in my group and we started playing it as a feature in itself and not as a distraction. The game itself is about a squad being hunted by a monster in the typical B movie cliché manner. Here’s the revised game with linked battle reports:
http://www.dakkadakka.com/wiki/en/Horror_Scenario:_Lurking_Terror