My humble thoughts and not necessarily law, just my observations.
Tulpas tend to manifest the darker parts of your subconsciousness and ego over time.
All parts of your being seek to have expression and experience.
We are programmed to seek out experiences in order to grow.
Our minds are used to create a balance between what is ‘good’ and ‘bad’ according to the moral framework we grow up in.
A tulpa, being an expression of yourself and connected to you, whatever impulses you deny will travel along the part of least resistance (Your tulpa connected to you and being an extension of your energy) in order to also experience and express itself.
So it can become the worse parts of you or the unfettered, unrestricted.