Rift Quest:To Hold Back the Inferno  

At each Tether, activate it to call Darius. He has over 30k hit points but he can die here, and if he does you lose and have to try again.

At the North Tether, you will fight three waves: two Obsidian Shardlings, three Obsidian Shardlings, and an Obsidian Hunk.

At the South Tether, the same three waves, but the mobs are different: two Lavaborn Fiends, three Lavaborn Fiends, and a Lavaborn Demon.