So a friend recently told me about tulpas, and sent me this article:

Opinion | Conjuring Up Our Own Gods

[Some] people attempt to make what can only be imagined feel real. They do this by trying to create thought-forms, or imagined creatures, called tulpas. Their human creators are trying to imagine so vividly that the tulpas start to seem as if they can speak and act on their own. The term entered Western literature in 1929, through the explorer Alexandra David-Néel’s “Magic and Mystery in Tibet.” She wrote that Tibetan monks created tulpas as a spiritual discipline during intense meditation. The Internet has been a boon for tulpa practice, with dozens of sites with instructions on creating one.

one of these sites includes

Tulpa.info

that explains that

A tulpa is an entity created in the mind, acting independently of, and parallel to your own consciousness. They are able to think, and have their own free will, emotions, and memories. In short, a tulpa is like a sentient person living in your head, separate from you. It’s currently unproven whether or not tulpas are truly sentient, but in this community, we treat them as such. It takes time for a tulpa to develop a convincing and complex personality; as they grow older, your attention and their life experiences will shape them into a person with their own hopes, dreams and beliefs. You’ll create a tulpa by imagining a person in your head, and treating them as a person. The exact mechanism is unknown, but as you give a tulpa attention, and believe it can be a sentient person, it will grow into one, and act independently of you.

As the NYT describes, Tulpas are an ancient construct, described in various Indian and Tibetan Buddhist texts as far back as the 4th century CE.

However:

In 2009, anonymous posters on the discussion board 4chan started experimenting with creating tulpas, and the community gained popularity through the emergence of the My Little Pony: Friendship Is Magic fandom.

Meet the 'Tulpamancers': The Internet's Newest Subculture Is Incredibly Weird

Why?