Well, I made this map awhile ago. It was just sitting around, and I haven't edited it in awhile. So, I'm going Beta with it.
The idea behind this is, kill an enemy, two take its place. Eventually, this leads to a truckload of enemies. So, you pick either a Marine or Firebat and battle against the endless armies of Hydralisks. Of course, killing one gets you cash, which you can use to upgrade or buy units. Yeah, there's a mission too. Buy an SCV and bring a Psi Emitter to a beacon to capture it... capture all of them to win.
Basically, you can get everything else by playing the map. It'll make sense, provided you READ all the text the map displays at the start. If you have any suggestions or find any bugs, please let me know.
Version Beta002» No more of the lazy burrowing hydras... they might burrow, but not in spawns, so there should be a lot less of those.

» Hydras will fight until they have less than 50 during the mass. The remainder will die instantly and they will respawn a new crowd of Hydras.
» No more picking up the vespene cubes at teleporters
» Hopefully no more of the double unit selection when units are next to each other
» Gave stats and name to Unsieged Tanks
» Goliaths will repair cheaper and faster
» Added a Supply Depot at the upgrade base