Necromancer: Call of the Underworld Fractured Peaks Priority Quest

In-Game Description

This is the unique Necromancer quest for Diablo IV. It becomes available after players reach level 25. Complete it to unlock a special skill.

Objective 1: Pray at the Shrine of Rathma
Interact with the shrine at the waypoint marker.
Objective 2: Collect Unbroken Bone - 0/12
Kill the skeleton enemies in the area and they should drop the Unbroken Bone items.
Objective 3: Find the cave containing the vile artifact
The cave in question is actually The Bitter Cave mini dungeon and it can be found in The Sallow Riverbanks area of Fractured Peaks.
Objective 4: Enter the Bitter Cave
After you’ve found the cave entrance, go inside to explore.
Objective 5: Open the Jar of Souls
Once inside the cave, head southeast and interact with the Jar of Souls on the pedestal.
Objective 6: Fill the Jar of Souls
You will be knocked back and then enemies will spawn. Keep defeating them to fill the jar. Eventually, the Elite Phantasmal Tyrant will spawn. They are a Banshee-type enemy and can come with a couple of nasty modifiers. Make sure to distract it with your skeletons and mages.