Rift Quest:Damming the Stream  

Enter Runic Descent on expert difficulty. Kill Atrophinius the Fallen, the fourth boss, and loot The Horn of Atrophinius. Use the Horn where this boss originally stood to begin the event.

Each of these mini bosses is the final rift boss of different invasions throughout Telara. They all have roughly 70k health and there will be a pause in between each fight to allow the group to recoup. The Amulet of Eternal Imprisonment must be used on each boss when they are below ten percent health. Make sure you group knows to stop DPS and allow this use or you might find yourself having to retry this event.