Q: So is this just DID/"multiple personalities"/other diagnosis/being posessed by an actual demon?
A: No. Daemonism is, at it's core, just about giving your (already existing) inner voice a cute animal form & personality. There are no inherent medical or spiritual aspects to it, at least to me. Others may disagree, so feel free to take it up with them.
Q: How does this differ from tulpamancy?
A: I'm glad you asked, because I've done both. I tried tulpamancy at three different points in time and failed every single time. Every time I tried, I just couldn't produce an entirely new being entirely separate from myself. It never spoke, it never "appeared" before my inner eye, it never did anything unexpected. I felt like a dumb idiot talking to nobody and expecting a response, like an idiot. I tried the methods, I tried the hypnosis audios, meditating, lucid dreaming, I tried everything. But that's enough about my failures.
I think one major difference between tulpamancy and daemonism is the intent: tulpamancy sets out to create a tulpa, a new being that comes into existence in your mind and becomes a fully formed person (or furry, or pony, or anime girl...) with their own thoughts, opinions, wants and needs.
Daemonism, on the other hand, is all about yourself. Your daemon is you, just on the other side of the same medal. It's nothing more than that, because it doesn't need to be. Daemonism is all about understanding yourself and dealing with your problems by imagining that you're discussing them with an animal friend who wants nothing but the best for you.
Another difference is the significance of interaction. A tulpa is created by and thrives off interaction. Talking to it and giving it attention is how you keep it alive, kind of like Tinkerbell. It can go dormant if you don't pay attention to it anymore. I'm not sure if it can "die" this way, the guides I've read weren't really conclusive on that, but in my experience, all three of my failed tulpas simply "vanished" the second I stopped trying to interact with them. It could be because they were too "young", or not fully formed yet (although I tried for months), but it really seemed like I had achieved absolutely nothing in the end. I always felt horrible for not trying hard enough, not talking to them often enough, not forcing (tulpa term) enough.
For daemonism, interaction is part of the fun, but not a requirement for keeping your daemon alive. Your daemon doesn't need to be artificially created and kept conscious by constant interaction, it's always there with you, chilling. Maybe that's why I was drawn to daemonism almost instantly after my failed tulpamancy journey - I no longer felt that pressure to interact and perform all these specific tasks for this being that literally depended on me to stay alive. Is that selfish of me? Maybe. But hopefully I've illustrated the differences well enough, even if they're just based on my own experiences.
My first introduction to daemonism was this tumblr post, which also talks about the differences between Tulpamancy and Daemonism. Give it a read!
Q: How did you meet your daemon?
A: As explained above, this tumblr post was my introduction to the concept. The linked site had a guide for finding your daemon, which I tried the same evening. Earlier that day, I drank a cup of coffee (this is significant) for the first time in years (I stopped because it gave me sleeping issues), so when I tried to go to sleep, I was stuck in this weird half-sleep dream state - you know the one, where you're all sweaty and your mind is racing with half-formed dreams - so in a moment of clarity, I decided to do the exercise and call out for my daemon. I still vividly remember seeing darkness, then a red beak tearing through it to reach me, and I knew that my daemon had answered. The beak had a very specific shape and color, and after some research, I decided that it belonged to a northern cardinal. We don't really remember how we settled on the name "Cain", but it likely just popped into our mind during a projection exercise shortly after the caffeinated red-beak-dream.
Q: You're using "we" and "us" to refer to yourself, do you consider yourself plural?
A: No. The use of "we" does not mean that I (the human behind this) claim to be plural, have DID or other medical conditions, and I want to be as clear as possible on that. For me, daemonism is a belief system that is not (and not intended to be!) provable, documentable or diagnosable by science. The relationship between my daemon and I is like two sides of the same medal - I am him and he is me, if I'm referring to both of us I will use "us" and "we".
Q: Do you actually think any of this is real?
A: Depends on your definition of "real". Are my thoughts real? Then my daemon is just as real as my thoughts are. Can the presence of my daemon be proved by the scientific method? No, and I don't need it to be. I don't care if you believe it's real, it will not change anything about my situation. In the end, I do know that I'm "just" talking to an imaginary bird in my mind, but that's what daemonism is, so acknowledging that is not a "gotcha" moment for me.