Tulpas

A Tulpa is a type of mystical or theoretical entity found in the folklore of several cultures, especially Tibetan mysticism: according to legend a Tulpa is an artificial being or "thought form" created by those who have either meditated for prolonged periods of time or mastered some ancient magic: this Tulpa is often invisible but may become visible if its creator is strong enough to will them into existence, much like the Golem of Jewish folklore a Tulpa was considered dangerous and often grew bold and out of control - it was not uncommon for stories of Tulpas to turn sinister and even violent as the entities took on poltergeist characteristics or (in extreme cases) became almost demonic and capable of physical harm to others.

Once a Tulpa grows mischievious or violent it is said that only its creator holds the power to erase it and as such it is seen as vital for them to do so, some tales say that those who fail to do so may even become the final victim of the Tulpa.

In Fiction
Tulpas have appeared in fiction outwith folklore, a more famous example would be in the X-Files: when a Tulpa was created to enforce the draconic laws of a suburban community leader and given life via trash (in a similiar manner to a golem) - this Tulpa was murderous but uncontrollable and ultimately murdered its own creator (parallelling the fables, in which Tulpas were notorious for being uncontrollable).