METAL SLUG 3

Note: You don't have to do the entire Mission 2 as a zombie, as it would be hard enough, anyways, set the "difficulty" to "1", reach the boss area where the searchlights are.

Once you're there, if you're in human form, shoot down 2 of the 3 zombie scientists and leave one around so that he can turn you into one. Once that happens, shoot that one down too and don't touch the Med Kit, proceed to the boss fight, but before you do, I'd advise to save here in case you mess up, then load to try again if you did.

Once you're in zombie form, use the grenade button to shoot out a blood stream that will arc upwards and will cost "1" Grenade count each time you use it, take down all the "Monoeyes" (big aliens) first before they get you, after that, the "Ten Commandments" (core of light) will appear and drop monoliths, jump and evade the laser pointer where they drop and use the blood stream whenever possible.