The developers describe the content like this:

This DLC may contain content not appropriate for all ages, or may not be appropriate for viewing at work: Frequent Violence or Gore, General Mature Content

Darksiders III - Keepers of the Void is included in Darksiders III Deluxe Edition

On a quest from Vulgrim, Fury must travel into the Serpent Holes to remove an ancient threat that resides there. All new locations, puzzles, and enemies await the chance to test Fury’s abilities. As a reward, she can unlock all new weapon forms for the Hollows as well as the biggest prize of them all: The Abyssal Armor.