Gehenna

Gehenna is the plane of suspicion and greed. It is the birthplace of the yugoloths, which dwell here in great numbers. A volcanic mountain dominates each of the four layers of Gehenna, and lesser volcanic earthbergs drift in the air and smash into the greater mountains. The rocky slopes of the plane make movement here difficult and dangerous. The ground inclines at least 45 degrees almost everywhere. In places, steep cliffs and deep canyons present more challenging obstacles. Hazards include volcanic fissures that vent noxious fumes or searing flames.
Gehenna has no room for mercy or compassion. The fiends living here are among the greediest and most selfish in all the multiverse.
Cruel Hindrance- The plane’s cruel nature makes it difficult for visitors to help one another. Whenever a visitor casts a spell with a beneficial effect, including a spell that restores hit points or removes a condition, the caster must first make a DC 10 Charisma saving throw. On a failed save, the spell fails, the spell slot is expended, and the action is wasted. (Source: DMG D&D)
Khalas- The uppermost layer, Khalas, was the most liveable of the four planes with many waterfalls cascading down the slopes, the largest being the river Styx. The Styx followed a rough path down the slope, fell for thousands of feet/meters, ran through twisty rapids before finally disappearing into underground passages. Steam rose into the infinite and empty black sky making the horizon glow a dull red. Khalas touched the Astral Plane and had connections to Hades, the Nine Hells, and Sigil. The portals looked like black chasms in the floor of deep underground passages. Markings on the walls would often indicate the portal's destination, if you could read them. This is the layer that Ilulla has her home on.
Chamada- The second layer of Gehenna was the most violently active layer with lava cascades thousands of miles/kilometres wide and city-sized volcanoes yawning open on the slopes. The air was foul with acrid smoke for 10 miles (16 kilometres) above the surface and would cause blindness to unprotected eyes and had the effect of a stinking cloud on the lungs. Below ground the air was fresher but stank of burning flesh and hair.
Mungoth- Mungoth was a land of falling ash and burning snow. The furnaces of this layer were fewer and farther apart, allowing ice and snow to build up in the darker places between active areas. Travelers had to brave the never-ending avalanches of wet snow and fiery rock. Underground passages were relatively safe.
Krangath- The fourth layer was devoid of any volcanic activity, even underground. All was dark and cold. The name of this layer meant literally "dead furnaces".
Inhabitants- The only creatures known to be native to this plane were the barghests, running through the rifts of Khalas and occasionally found in smaller number on the other layers, and the pyroclastic dragons. All the other creatures originally came from the adjacent lower planes, mostly to hide from more powerful beings that wished to enslave them. Gehenna was often a plane of exile for the less powerful archdevils and daemon taskmasters. (https://forgottenrealms.fandom.com/wiki/Gehenna)

Alternative Name(s)

The Bleak Eternity

Type

Dimensional plane

Location under

Outer Planes

Owner/Ruler

Ilulla

Ruling/Owning Rank

Goddess