I think it would be a crystalline like creature that would over exaggerate the appearance of it's victim's reflection when the victim were to look into it and then it would praise the victim into feeling self entitled.
Some of the monsters are more effected by the disorders they pass on than others. This monster isn't mean- it passes on Avoidant personality accidentally. Some monsters are more evil, and give the disorders to get something out of it.
why did you created esspecially this monster in a non-mean way? Is it because ppl with AvPD are also missunderstanding words as mean others say to them, even when the people who said it didnt meant it in a insulting way? Or I'm wrong?