Hi. The author is sorry this has barely been edited, it's actually very late as the author is doing this. When this posts, he will likely be unable to access a computer, so he's set it to post automatically.
Sometimes referred to as the Pilgrim’s War, the Holy Settlement Crusade was an attack by the Grand Sanctum, a semireligious state that decided it would be easier to conquer the Fourth Timeline, still recovering from the Dead Messengers, than it would be to actually find and terraform a suitable planet on which to build their empire. Their relative experience with magic allowed them to compensate for much smaller numbers of actual mages, and one of the most important factors in this were the Glass Soldiers.
Glass Soldiers are hard counters to almost all of the widespread Fourth weaponry, being almost completely immune to lasers or electricity, highly resistant to fire, only slightly more vulnerable to cold, impossible to properly target with Bloodforged weaponry, and prone to shattering into fast homing projectiles when actually hit, although they are remarkably durable. They were also impossible to truly kill without destroying both cores, located in the head and chest cavity respectively, which would each repair the other if damaged. Severing the connection between the two (via decapitation) would force them into a dormant state until they reconnected.
Unfortunately, even death will not immediately depower the glass, and will cause the main body to shatter explosively, often killing the one who actually destroyed their cores, considering the ranges generally necessary to do so.
Comet Shards are one of the few things that can consistently destroy them with relative safety, but only individually, in larger groups the splinters often reach sufficient density to penetrate the heat cloak. The other consistently effective weapon is Thunderbrand, which can shatter large groups of Glass Soldiers with single castings, while destroying both cores simultaneously. The large Fuel cost and the chance of collateral damage or friendly fire limit its usage significantly, however, although perhaps not as much as they should.
Lastly, their biggest advantage is likely that they can be mass produced fairly cheaply over a span of hours, including cores, ultimately requiring a bit of sand or glass, found in abundance on beaches or in deserts, a bit of copper, and a bit of iron, both found naturally in dirt, or, if more speed is necessary, the appropriate types of ore. After production, they could be deployed almost instantly by teleportation, and recalled in the same way. Led by mages for fire support and field command, they were very effective, to the point that most of the reason the Sanctum actually lost can be pinned directly in assistance from the Fifth.
With access to an Omnicrafter Ring, Glass Soldiers can be given simple upgrades in the form of eye gems, granting minor supplementary abilities based on the elements the gems are formed from. While the gems were relatively difficult to get ahold of, they could drastically improve effectiveness, such as Steel Gems to make them more durable, or water gems to make them flexible and good at swimming. The gems are interchangeable, allowing excellent versatility, and as a whole Gem Eyed take the role of elite soldiers, albeit expendable ones.