I've spent some time camping a couple of
https://wiki.project1999.com/Illusionists_Stone
with the intent of being able to use it to sell to merchants on my iksar. I noticed I cannot use it in felwithe though. It gives the notification "Illusions do not work in this zone" or some such. But you definately can cast illusions in there, as druid in wolf form, necro as skelly, enchanters in ANY of there forms. Not sure why it's relegated to not working in felwithe, north or south.