The Underworld

A plane of existence that the wicked souls of the world are said to be sent to, those who make deals with the Fiends hailing from here will meet them in the afterlife as well. While the Underworld is said to consist of multiple layers, it is, in fact more like a hellish version of the mortal plane, and the strong negative energies tend to attract the souls of unscrupulous individuals after their death. It can only be accessed by the living in three ways: through a portal created by an incredibly powerful Warlock or Sorcerer, through a portal created by a Celestial, and through death after living a wicked life. The Underworld holds several areas within, and how one lived decides where their soul will appear. Lesser Fiends such as Imps often roam these areas, hoping to trick and further torture the lost souls within.  

No Rest for the Wicked

The eternal battlefield of Tartarus is where those who actively and willingly used any form of physical violence against the innocent will find themselves. It is a place of never-ending war: the wicked will be forced to enlist, compelled by their Fiendish generals to forever battle without any rest or respite, and their victims are not given any armor or other protective gear. Thus, they are forced to die in agony on the battlefield constantly. This cycle eternally repeats. Fiendish torturers scour the battlefield for the incapacitated, hoping to drag their prey into their torture dungeons before they can regenerate at the start of this cycle. They deeply enjoy inflicting unspeakable horrors, and utilize torture methods beyond mortal comprehension. Their ruthlessness does not merely end at inflicting physical and mental terrors: these Fiend torturers are able to flay one's soul within inches of disappearing, only to wait for it to regenerate before continuing to torture their victim. Fiend sergeants patrol the battlefield, looking for dissenters to incapacitate and deliver to these torturers.   The Mire of Lost Souls, however, is a swamp from which there is no escape. Those who consciously and willingly misled others in life will find themselves at the entrance to this area. They will then be ordered by a Fiendish overseer to find an artifact, under threat of a century of uninterrupted torture. However, the artifact requested never existed in the first place: the person will forever slog through the Mire, looking for an item that never was. Trying to find the entrance in order to escape would be in folly, as this is impossible: once the gates close behind the individual, they can never find it again. The Fiends are able to summon it in order to travel from the Mire to other areas of the Underworld, but often refuse to. Those who have made deals with Fiends in life will often find themselves here, hopelessly looking for a way out. Fiend scam artists tend roam the area, offering false deals for escape with steep prices: once their victim agrees, they will make of with a piece of their soul, never to be found again.   And while the Grand Hall sounds like respite from the rest of the Underworld, to see it as that would be foolish: those who willingly practiced cannibalism outside of extreme survival situations and those who denied others food in times of strife while having plenty themselves will find themselves here. The only guests allowed to eat in its mess halls are the Fiends who visit the Great Hall: The mortal races who find themselves here are forced into ovens, only to be fully conscious while the chefs slice them into pieces, only to go through the torturous pain of being a meal to the Fiends once served. Then, they will revive to experience all of this over and over again for all eternity. The chefs in its kitchen are said to cook the meals for none other than Azdar himself, and the most wicked in the Great Hall will find themselves served to him. Should one of the mortal races be placed at the table, they should not see it as mercy: their arms will be splinted with wooden slats, and they will be ordered to eat under threat of being boiled alive in oil. Naturally, the victim will fail.    

Abandon all Hope, Ye who Enter

While one could think that they could survive the Abyss by avoiding these three areas would be wrong, as the rest of the Abyss holds non-physical threats. If a person's soul is destroyed in the afterlife, they will be struck from all existence: nobody in the world of the living will remember them, any written record of them will never have existed, and even their family will not remember that they ever were.   [lawless city with a fiendish market: lies near the Great Hall. The greedy and those who stole from the vulnerable are transported here: everything costs a piece of their soul, and Fiendish thieves roam the place,trying to steal the items to force the victim to buy it back. These work for the Fiendish salesmen, who try to trick the lost souls into destroying their soul this way]    

At War with the Mortal Races

While Fiends are known to not fear mortals as they see them as lesser than themselves, they do seem capable of fear, since they constantly dread meeting one legendary warrior... The Fiends have never met him, but Azdar and his archdevils have viewed events from beyond the world veil: there is one Human warrior they fear, and even mortals who have heard the tale doubt whether this man is a Paladin, a Barbarian, or both of these. He does not speak or bother with other mortals, and it is said that he once razed the entire Underworld to the ground in a copy of this universe. He had even slain Azdar in that world, with only a crossbow... In that world, the Fiends manage to invade the mortal world, and caused terror on the mortal races. However, from one family, a hero would arise: having lost his family to the Fiend attacks made him swear vengeance on the attackers. But losing his pet rabbit in the fray truly caused an unending rage and unending hatred of Fiends within him. He is said to not talk much, and he doesn't pay the mortal races much mind in his pursuit of the Fiends: he is strong enough to tear a lesser fiend apart with his bare hands, but the mortal races in his way are gently shoved aside at worst. However, he did not perform these incredible feats in the name of any deity. Thanks to these tales, it is said that the Fiends of the Underworld fearfully steer clear of rabbits to this day under orders from Azdar, fearing that the death of a rabbit might accidentally trigger their eradication in this universe... The mortal world might only be safe from an all-out invasion for this reason. However, this information caused the Fiends believe that this man was a Paladin, resulting in their characteristic hatred of Paladins and Clerics.