A tulpa is nothing more than a section of your consciousness that you've created by your own will and made autonomous through giving it attention, teaching it about the world, and basically raising it like a child. There is absolutely no spiritual or religious connection to tulpae and this is a very common misconception. A tulpa is your own creation. No force, evil or holy, has any part in the creation, actions, or thoughts of a tulpa. I would know. I have created several over the years good, evil, and neutral. Some are no longer with us and some prefer to exist in solitude, but I can assure you there is no Devil at play in anything that has to do with tulpae, and you are the only God in terms of its creation.
Refer to tulpa.info for real information from others who have done this most or all of their lives. Ignore any nonsensical trolls, bronies, and members who constantly ask stupid questions even after getting the correct and factual answers on the forums. I highly suggest reading the faq and articles on the main site before even trying to look at the forums.
Not meaning to rage out or anything, but the truth is the truth. Creating a tulpa is a completely conscious act on your part. There's as much truth to a Devil creating or controlling your tulpa as there is to the fantasy spells here working (hence the term "fantasy").