Tulpa (Imaginary friends on a whole new level)
You know how they say that if you concentrate enough on something it will come true?
Tulpas are kind of like that. With enough time and concentration, you are supposed to be able to create a being, only bound by the limits of your imagination. It would be visible to you and act independently (within the bounds of your subconcious I would assume). But the time and effort needed to succeed is tremendous, aka something you say so that when people don't succeed, they can't say it's fake.
Personally I'm half sceptic, half excited. Even if it would work (since you are able to hallucinate) I don't think it would be very healthy. Imagine, though, having your own imaginary mythological creature companion. Wouldn't that be fucking awesome?
Here's a guide on how to create one: http://tulpa.info/guides/faqman-creation-guide.html
Also, here's a creepy pasta: http://creepypasta.wikia.com/wiki/Tulpa
I will not take responsibility for any loss of sanity or accidents. I am just simply informing you of this very interesting phenomenon
If you were to create your own Tulpa, what would it look/be like? Would it be a dragon? A loli? A voice without a body, telling you to kill everybody?