Glad someone had a look :-)
In this version if two of the nasties collide then one of them is teleported to an empty space.
The levels are totaly random in that it uses a code to set the amount of nasties the first level is code 15, the first char is the number of reapers ie - 1 and the second is the number of nasties plus one ie 6 there is also an equal number of land mines as nasties. the code is incromented by one each level so you get a steady increase until level 84 where it will do silly stuff.
Updated the zip to v1.02 - I think I have fixed the bug where you started under a nasty, I've also stoped it using full screen(it flickerd too much on start up)