Alright, this isn't as challenging as the first boss fight. Three to Four Dark Matter Gun shots on the first form of the Makron will hopefully kill him if they are good shots. If not, switch to homing rockets or the nail gun. His second form gets a bit trickier, try to conserve rockets and use the Dark Matter Gun though, you'll need a ton of rockets for the end. Just strafe jump and hide behind the pillars, emerging to nail him with the DMG whenever possible. The Brain form is once again easy, shoot the top of the brain by the blue pillar with a rocket, then unload as fast as you can into the brain. Rockets are generally found in the corners of the top if you run low on health. Be sure to keep moving when you are on top though, on General the units that spawn are much more deadly, such as the Heavy Tanks, Judges, and strogg infantry with Railguns. Save everytime you kill one form of the boss with as much health as possible, you will need at least 125 health and 50 armor to beat the brain easily, if not, repeat until finished!