>>111200A tulpa is pretty much you roleplaying with yourself, but to such a degree that it feels believable (with the tulpa having its own viewpoints, opinions, etc.), thanks to practice and mental techniques. Unless you believe in /x/ type stuff of course.
It's about as sentient as you are, because it's just you but having trained yourself to converse with yourself from another perspective. It's not all that different from fantasizing about doing stuff with your parasocial love, and imagining what he does, says and thinks - based on your understanding of HIS perspective and personality, but still ultimately conjured up by YOUR mind and fully in your control. A tulpa is really not too dissimilar from taking this to its logical extreme, making it much more immersive but the principles are not that different. In particular, a tulpa's personality, appearance etc. are going to be exactly what you want them to be: it's not going to be a "real relationship" in the sense that it's never going to be a separate sentient being with the ability to disagree with you or do stuff that you find retarded.
Disclaimer, I don't have a tulpa, I've just talked to some schizos, so this is secondhand understanding.