The Harrowing

From Kickstarter:

This expansion includes additional maps (including an excursion into the realm of Sheol), new monsters, and legendary magic items that have been forgotten even by the eldest among the celestial hosts. This expansion also includes a brand-new, exclusive Warlock patron: the Horseman. Last but not least, "The Harrowing" is a mini-adventure for players of level 12, which can be seamlessly inserted into the main campaign, or played as a standalone adventure. This adventure sees the party venture into the Realm of the Dead for reasons that will soon become clear... but whether they can escape the unholy horrors that they find there remains to be seen.