Zorn

No one knows what a Zorn really is. But everyone knows, what it isn't. It isn't like any other creature in Britannia. Zorns seem to defy the very laws of nature and logic. Some say, they are the antithesis of everything. They simply walk through walls as if they weren't there. They negate all magic around them. And they disappear, should they be slain. The Zorn is a horrible foe, to be avoided at any cost.

Thankfully, they can be only found in the deepest dungeons.

Zorns only appeared in Ultima I and IV, it is unknown what happened to them after that. One can assume they were wiped out of existence by the cataclysm that created the Underworld.