Vesalius

Vesalius is a Rift Guardian, only encountered in Nephalem Rifts as a random boss. He is a variant of Vidian.

Vesalius retains the two basic abilities of Vidian: Typically, Vesalius will not attack in melee and will instead use Gateway to keep his distance. He also gains two more affixes to make moving around the battlefield as complex as possible: Both affixes get lower cooldown as the boss loses more and more Life.
 * Energy Barrage: the deadliest of his attacks, a very hard to dodge spray of bolts in rapid succession that ignore cover. Unless moving at high speed, can kill an adequately geared character in one volley.
 * Gateway: allows Vesalius to disappear into a portal, then reappear at any other location.
 * Wormhole affix
 * Frozen Pulse affix

He does not retain any of the advanced abilities of Vidian. However, despite his apparent simplicity, this is a very challenging boss, and without a good portion of movement and protection, can easily dispatch an average player.