I actually did some research on this topic. The stories you hear about tulpas are mostly bullshit, but there is a real thing called that that's quite interesting. Basically, there are a few things that combine:
- It's disturbingly easy to get the human brain to hallucinate something. It's a common side effect of mental illnesses and drugs for a reason, and studies show that practically all children hallucinate regularly, and even sleep deprivation induces it. It's not all that surprising the right meditative technique can do it as well.
- You know that thing where you're writing or roleplaying, and one character is so easy to write that it becomes automated and almost writing itself.
- It can be argued, according to some philosophical theories, that the only criteria for personhood is behavior, not any technical "realness" or having a body
So basically some people imagine a character, make themselves hallucinate it, and automate the control of it so much it feels like it's acting on its own. And they don't put in a forth wall. The result is not really anything much more than you'd expect from those components, but has interesting philosophical implications if you're into that kind of thing.
Basically, a tulpa is as "real" as a dream. There are plenty of people that argue that a reoccuring dream character that seems to act consistently and keep memories of previous dreams as a person as well. A dream is a fair bit more "real"-like than a daydream or visualization, if you consider realness to be a fluid thing.
Me? I mainly consider inducing hallucinations like this dangerous and avoid it for the same reason I avoid hallucinogenic drugs. *Most* people I've seen with tulpas seem to enjoy the experience, but a bit to many are out of touch with realty for it to seems safe. As for "realness" and "person" those are just words humans made up, and I just go straight to the raw math of utility functions and game theory where there is no need for them to determine my actions.
Tulpas mostly have properties associated with "imaginary" things such as not having a body and only being able to communicate with one person, and others associated with "realness" such as being able ro provide comfort, ure loneliness, and have ideas attributed to them. Basically, if "not-real" is mammals and "real" is everything else, tulpas are the platypus.