A tulpa, of which you may be more familiar is the likes of the parking fairy. She exists because people believe in her, they insert both thought energy (electrical capacity) and emotional energy (magnetic potential) into the creation of her. Doesn't happen right away, it takes a lot of repetitions of this micro second alignment of heart mind and soul in order to create her. After ten years though, you know she is real and she works for you better and better as time goes on.
Eggreggors are similar however it takes less individual potental in order to create them, it is created by grouping.
Like, hell, it never existed, until the bible created the idea, and people invested both thought and emotional energy into it.
In order to give it, or any finctional character a 4th dimensional place of resonance however the grouped thoughts have to be aligned. So if there is one book lets say telling one version, and another book telling a different version. Both characters will become real but they will only be real for the ones who believe in their version of the book.
This is why religion was the first to divide god into parts and versions. Each version of them exists because each version has millions of people painting the same etheric image of them.