@nyomuponyo Usually splotches are shadow quality issues. If you're rendering in Eevee, you can go into shadow settings and increase the stepping, maybe volume shadows? Maybe set to use hq normals.
If you render this in cycles and you still see those splotches there might be a model issue.
Probably the best resource to learn fiction writing on YT. Especially if you are interested in speculative fiction. I love Sanderson's style of teaching and the fact that he makes these available for free is incredibly based.