Extra-dimensional shapechangers that lurk in the half dimensions hidden behind mirrors. Believed to possibly be bizarre aberrant mutations of doppelgangers. They make their home on the Plane of Shadow and slip into the space between that plane and the Material World, which is accessible by mirrors. They copy creatures they study through mirrors and they can crawl into any mirror as if it were a door or window and instantly transport themselves into another mirror within hundreds of feet, even diminutives shards of one. It can only exit a mirror if it is using its shapechange ability to take on a humanoid form. Its copy is always a mirror image of the original creature.
They explode into jagged shards of glass upon dying (20-ft. radius spread). They can cast mirror image, open/close, and mage hand, and have mild resistance to acid and fire and are vulnerable to sonic damage. They have a small bit of fast healing. They are not generally very challenging, but the Soulsliver encountered in Fort Hailcourse probably had some class levels.
First Reference: Chapter 58
Other Notable References: —