Journey of the Daggers (The Complete 2012 Trilogy)
The Cubit (capital C) is the device which produces cubits (lower c). When a person touches the Cubit, a physical duplicate emerges from the Cubit (though not always immediately) that hunts the original person down, kills them and eats them, thus removing the original from the world. Taking the original’s place is the evil twin, a doppelganger of sorts. These cubits are so well disguised that few know the difference between the two, but there are signs, particularly during the early stages of a cubit’s development into its original’s personality.
Another defining event that reveals a cubit is when the Master of Evil (Satan, Lucifer, Devil, etc.) takes control of it. In these instances, a physical change takes place in a cubit’s eyes. They turn crimson and the pupils roil with silver sparks and jags.
All cubits are virtually invincible. Even mutilation will only produce another from the Cubit. The only way to kill a cubit is with a Creation Dagger. Additionally, if an original can kill a cubit before it kills the original, that person can longer be affected by contact with the Cubit.
In the history of the Fifth Age, cubits have been responsible for many of the lost civilizations including the ancient Maya and the Anasazi. Their near perfect resemblance of the original makes it possible to seamlessly integrate into any culture.