Activated Vessels are the creatures Dark Vessels transform into if they successfully summon a demon into their own bodies. They are one of the more disturbing monsters seen in Diablo III.
Activated Vessels are not the stereotypical possessed human, they are humans, possessed by demons, Diablo style. They appear as severely mutated humans who have spikes, sinews and blood all over their bodies.
From the concept art, we can see that a spike under the neck is called the Teeth of Diablo. This may mean a special skill associated with the aforementioned spike, perhaps some kind of leeching attack.
|Diablo III Bestiary|
|Bosses||Skeleton King • The Butcher • Maghda • Zoltun Kulle • Belial • Ghom • Siegebreaker Assault Beast • Maiden of Lust • Azmodan • Rakanoth • Izual • Diablo|
|Human||Dark Cultist • Dark Summoner • Dark Vessel|
|Demon||Activated Vessel • Armored Destroyer • Dark Berserker • Hellion • Imp • The Fallen Ones • Treasure Goblin • Winged Molok • Vile Hellbat|
|Undead||Crawling Torso • Dune Dervish • Ghoul • Grotesque • Risen • Skeletal Executioner • Skeletal Shieldman • Skeleton • Skeletal Archer • Tomb Guardian • Unburied • Walking Corpse • Wraith • Wretched Dead • Wretched Mother|
|Beast||Beast • Carrion Bat • Carrion Nest • Dune Thresher • Lamprey • Scavenger • Goatman • Goatman Shaman • Desert Wasp • Quill Fiend • Wood Wraith|