Skeleton Soldiers appear somewhat late in the game, during Chapter 3.They're incredibly weak. However, they have an advantage- They attack in huge swarms. If a Maso Commando is nearby, he'll set them aflame, making them twice as fast and twice as strong. They look like WWI soldiders wearing gas masks, and wield bayonet-rifles. They come in two flavours, and two different looks- The melee versions simply rush you and try to stab you with the bayonets. They're incredibly common and the best way to deal with them is to send a rocket or a grenade to the center of a swarm and gib about 20 of them at one time. The second version tends to appear after a swarm of the first version. They're a bit taller then the melee version, and actually shoot at you with the rifles, as well as throw smoke grenades that poisons you for a bit, similar to the second Devil Monk variant. What's interesting to note is that this poison can even damage you in Demon Morph, so be cautious. If you see a small can on the ground emmiting smoke, stay away from it. The first kind encountered wear flat dull olive uniforms with bloody gas masks that have blue-tinted glass. They also, interestingly enough, have a hole in their chest. The mask's air tube goes through it. The second kind, encountered in the Military Base, wear modern desert camo (the Military Base ahem*Area 51* is in the Nevada desert), along with integrated NVGs which emit a green light. They still have a hole in their chest, however. Both attack variants exist for both kinds of Soldiers, so there's no difference between the troops that rush you in the Train Station and the soldiers that rush you in the Military Base. Handle them the same way. All of them last only a few seconds in death, so its very hard to air-juggle them for gold.
Due to their old-look and blitzkrieg-rush tactics, they may be based off of soldiers that participated in ill-fated trench-rushes during WWI, that got millions of soldiers killed, which explains why there's so many in Purgatory. The cans they throw could be poisonous gas used for chemical warfare, such as Mustard Gas or clorine gas.
Skeleton Soldiers appear to be the ones that man the mortar turrets encountered in the Military Base. What's even more interesting is that its the older version and not the more "Modern" soldiers encountered in the same level. They also make the sounds a Maso Commando would make when killed. They also last a lot longer when killed, and you can get gold from them by juggling or stake-juggling them.
When shooting-variant Skeleton Soldiers are lit aflame, they will act just like melee-variants until the flame dies out.
Sometimes, Skeleton Soldiers will have enough of the Maso Commando lighting them aflame, and will try to kill the fugly tard. Its rather amusing to watch 20 Skeleton Soldiers attack a single Maso Commando and be completely unable to kill him. Often times he will just keep lighting them on fire, but sometimes he will launch a grenade and kill most of them.
Bizarrely, the Skeleton Soldiers located in the Abandoned Factory are even larger then usual. They are not any stronger then normal, however.