Adder Stone

An Adder Stone is a stone with a naturally occurring hole in it barely large enough to fit a finger through. The in-game art varies in what kind of stone it is, though appears to most often to be some form of Green Serpentine[citation needed].

Effects
By using an Adder Stone your vision is restricted to only what you can see through the hole. While doing so, however, your character can see and make perception checks against magically hidden entities, such as secret doors and invisible creatures.

Looting
The Adder Stone is considered a Rare Drop, but this can be lowered to Uncommon by killing monsters with the Fae type. It's also commonly believed that Adder Stones are more commonly found in Coeden, but there are no effects in the files to prove this.

Crafting & Repair
Adder Stones can not be crafted, and any attempt to alter them via crafting results in an "Artificial Adder Stone", which has no effect at all. Luckily, using an Adder Stone does not reduce its durability, so there's no need to put it in the crafting system anyway.

Trivia

 * There was originally going to be only one Adder Stone to be found in each of the 20 faces of ANNWN, but this was quickly changed after their implementation back in v0.1.2.
 * Adder Stones are based in real-world European mythology, where they are also referred to as "Witch Stones".