I am looking for an intelligent monster that is linked to the plane of shadow, but is not evil. It has to be able to create illusions, e.g. so that shadows on walls, floors etc. can be changed (silent image or better). It has to be invisible in bright light, so that it only appears when there are shadows. It can be incorporeal, but this is not absolutely necessary. Preferably it should not be an undead. And preferably it should have a CR in-between 6 and 8. Does anybody know which monster fits this description?
Sounds like you want a pixie with the "Dark" template added. That's the simplest.
Or if you want something more complicated, check out the Ravenloft supplement White Wolf did a while ago "Van Richten's Guide to the Shadow Fey."
A dark pixie or shadow fey sounds good. It fits right with the atmosphere I was looking for. Thank you.
Where would I find this dark template? I've searched for it but apparently I'm to stupid...