The Dying World
Drop: signets, dark sapphire, crimson quartz, spirit crystal, greater charms, Harbringer of Death, stardust
Mortis is the final boss of Dying World and original Reckoning. He barely has any need to team up with someone else to deal with multiple opponents. Only enter if you are really looking for heavy fight, otherwise you will just end up rage quitting. This map can be entered if you finished hell difficulty.
Craft black rune with tome of town portal to enter this map in act 1.
Best charms can be obtained here, Harbringer of Death is a set scythe, which has also another function to it; stardust is what most people will be after now, it upgrades almost all demonic items or gears of fate (celestial refinery excluded).