I went looking for the book, and had problems finding it. It seems that DMs Guild (and most other online stores) call it Advanced Races 2: Darakhul Ghouls (Pathfinder RPG)
, although that's not actually what it says on the cover. The cover picture makes it look like the book is called "Darkakhul".
Anyhoo, here is the blurb, from the DriveThru page for Advanced Races 2: Darakhul Ghouls (Pathfinder RPG)
DriveThru RPG wrote:Advanced Races 2: Darakhul Ghouls (Pathfinder RPG)
From Kobold Press
Can you master your hunger and adventure among the surface dwellers? Or will the monster within claim you?
In the lightless depths beneath the ground, an empire of devouring ambition grows and plots and dreams. They call themselves The People, but the rest of Midgard calls them the Lords Subterranean, the Ghoul Imperium, or simply the Empire of the Ghouls. Their cities lie out of sight. Their goals know no limits.
To them, if you are not a member of the People, you are food.
Advanced Races: Darakhul
gives you everything you need to play as a darakhul, a greater ghoul of the dreaded Imperium. This 18-page sourcebook by award-winning designer Ben McFarland includes:
- 11 new darakhul racial traits, and 14 ghoulish feats including Eater of the Dead and Undead Rage
- 3 new archetypes: Quicksilver Alchemist, Imperial Hunter Ranger, and Necrophage Wizard
- 8 revolting magic items and equipment
- 6 new spells and incantations
- Survival tips for adventuring ghouls
- Haunting art by Guido Kuip, William McAusland, Chris McFann, Hugo Solis and Darren M. Calvert
- And much more!
Just remember, your fellow party members are not food! Yet…
Looking at this, I think the biggest challenge with using Darakul ghouls with Ravnloft is that they are tied into this Ghoul Imperium. You are not just getting the rules for playing ghouls - you are getting this organisation that backs up their existence. I'm not sure how much detail on the Empire of the Ghouls would fit into the 18 pages of this PDF (and I don't know if there is more detail in one of the Midgard books) but I'm thinking that you probably need to lift that entire concept and create a bespoke Ravenloft domain based around the Lords Subterranean.
I suppose that if you wanted to retain the Midgard tie-in within this book (instead of throwing it out and adding in local people that are like the ones in Bavaria) you could have an area of Midgard get sucked into the Mists of Ravenloft and become some sort of crossover between Ravenloft and Midgard.
And if you did go with "Midloft" or "Ravengard" or whatever you wanted to call a crossover, you could dip into whatever the Midgard canon said was above the area of the Ghoul Imperium and ramp up the horror aspect by adding in plenty of Ravenloft rules.