Train Station, Abandoned Factory, Military Base, Hangar, Magazines, Refinery, Dead Warehouse
Maso Commandos are advanced enemies that appear exclusively to Chapter 3, always appearing alongside Sado Commandos and Skeleton Soldiers. They look like big, muscular men that wear muscle shirts, (oddly enough) sneakers, short pants, and blood-stained gloves. Their heads have odd rods sticking out of them, which contorts their hideous face, and their backs are torn open, revealing their spines. They're advanced because they can boost the power of Skeleton Soldiers, making them twice as strong. They attack at close range with a flamethrower, but this is easy enough to avoid. At long range, they'll chuck grenades at you. Clearly, this is the more dangerous attack, so keep moderately close to them, just out of range of their flamethrowers but not far enough for them to switch to the grenades. They're immune to almost all weapons, except the Freezer gun and the Stake gun (On easier difficulties). Use anything else on him he'll simply laugh at you as you fire away and waste ammo. The best way to take them out is to either shoot their gun, which causes them to explode violently, so be careful, or to freeze/shatter them. On easier difficulties, you can also stake them and kill them instantly without having to worry about either the explosion or wasting Freeze ammo.
They may be based off of either high-up soldiers thinking they are invincible, or (as a stretch) experimental military technology.
They are the Sado Commandos counterparts. While Sado Commandos represent sadism, the desire to inflict pain on others, Maso Commandos are Masochists, who take pleasure in experiencing pain themselves, which is probably also why the laugh at most attacks.
They have "I love mom" written on their shirts around their stomachs.