Invisible Stalkers

These deceitful beings use their natural invisibility to sneak up on their foes and strike them down from behind; however, apart of the obvious problem of being somewhat difficult to spot, they are not very strong.

In Ultima I, (when they were known as "Invisible Seekers"), they were entirely invisible to the naked eye. In Pagan, however, their red glowing eyes could be seen, but their outlines would flash briefly when struck in combat.

During the First Age of Darkness, they were encountered only in dungeons. In Ultima VIII, they are found on the Plateau (and sometimes elsewhere nearby).

Notable encounter
In a cave on the Plateau, invisible stalkers guard a big door. That would have been the door to The Lost Vale.