Mitestone

Mitestone is a material in Louse. It is used to make the masks that the Pilgrims wear.

Properties
It is unknown what the origin of mitestone is, or what its exact properties are. However, it is known that it is a stone of some kind, and is capable of being carved into masks, as the Pilgrims have done. When Null carved the mask they made for the Old Friend, they were at their workstation, which was in a windowless room. It is unknown if this workstation is where all mitestone masks are made, or if it was specifically Null's workstation.

When worn or used, mitestone induces strong emotions. Null's mitestone mask put them into a state of relative tranquility; however, when it was shattered and a shard was picked up, they felt an overwhelming fury course through them, which they had never felt before then. This fury took complete control of them as they murdered the two unnamed pilgrims with them, only faintly hearing their screams. This overwhelming fury is felt every time they use a shard of a mitestone mask, regardless of the mask in question. Multiple spawns of Rot also use mitestone masks, including the Love of Rot and the Sound of Rot. The Sound's mask appears to be the same style as the masks of the other pilgrims, and may even be the mask that Null made for the Old Friend. The Love's mask, however, was different in style; it had multiple holes and gaps in it, with those making up the face instead of any carvings. It is unknown why the Love's mask is different from all other masks seen thus far.

Turmoil did not recognize the material the masks were made out of, despite multiple Rot creatures wearing it.

Theories
If Null's mask is indicative of all mitestone masks, then their primary purpose may be to induce a feeling of tranquility for the Pilgrims that go to find Rot. This would match what the Love told Null, which is that resistance is what causes pain; the masks may be intended to allow for a peaceful, painless assimilation into Rot. If this is the case, then shattering the mask may invert its effect, resulting in the overwhelming fury that Null always feels.

It has also been theorized that the mitestone masks are what allow Rot to control the various growths of Rot, such as the Love and the Sound.