Zorn

Zorns are a bizarre breed of magical creatures, seen briefly in Sosaria and later in Britannia. Known as "antitheses of everything," the zorn were capable of a number of unexplainable behaviors. They appeared in Ultima I and  IV.

Description
Zorn bodies consist of a large semi-spherical node supported by three legs. Their mouths are situated on the top of this node whereas their sensory organs are positioned close to the ground. Through means unclear, zorn are capable of physically transcending all known matter - passing through obstacles as though they didn't exist. This strange negation of reality also appears to effect the ethereal waves surrounding this beasts, as magical arts are disabled in the immediate vicinity of zorn. Commonly found in subterranean locales, these omniphagous entities have long puzzled scholars, as the evaporation of their physical bodies upon death has left little means of studying the zorn. They have occasionally been found in the company of the normally xenophobic gazers, although their purpose in this seeming alliance has never been discovered.

These enigmatic creatures faded from human sight shortly after the completion of the Quest of the Avatar, but whether this vanishing was due to extinction, migration, or other causes has never been determined

Trivia

 * Zorn are very likely derived from the xorn of the table-top role playing game,  Dungeons & Dragons. These creatures appeared in the Monster Manual published for the game in 1977, and appear similar to their counterparts in Ultima, possessing a similar trilateral radial symmetry to their form and a capability to move at will through stone and minerals. Both Zorn and xorn furthermore are said bear a resemblance to the three-limbed  Asag, a Sumerian demon which featured in the poem Lugale.
 * Zorn were to be included in the canceled Ultima X, where they appeared to have adopted the geophagic behaviors of the Dungeons & Dragons Xorn. See Planned Monsters for Ultima X for further details.