Malbolge

From Fiendish Codex II: Tyrants of the Nine Hells (3.5e):

Until recently, Malbolge was the hardest layer of Baator to traverse—a never-ending slope bouncing with eternally rolling boulders. Since its recent change in management, it has been transformed to the point of unrecognizability.

Less than a year ago, Malbolge was the only layer of the Nine Hells not ruled by a devil. Instead, it was governed by Malagarde, the Hag Countess—a powerful night hag chosen as ruler by Asmodeus himself. The appointment of such a creature to rule over devils occasioned much quiet grumbling from many diabolical entities who considered themselves infinitely more suited to the post. Why would Asmodeus name a nondevil to rule in Baator? The answer, as it turned out, lay in his volatile relationship with his insolent and mischievous daughter, Glasya.

One morning, the Hag Countess had just dodged an oncoming boulder and eviscerated a squirming lemure that had displeased her when she was wracked by terrible spasms. She collapsed to the eternal slope, shrieking in agony, and for a moment it looked as if the Lord of the Sixth would simply roll off the layer and into the devouring void just past its edge. Then the land, too, began to convulse with earthquakes, and the tunnels beneath its surface turned themselves inside out. The Hag Countess's most loyal lieutenants were crushed by falling rock or swallowed up by the hungry earth. Then the infertile soil of Malbolge seized the countess herself by the wrists and ankles and held her fast while she underwent a transformation even more shattering than the one destroying her land.

The Hag Countess began to swell. First she grew as large as a giant, then as big as a titan. Shuddering and howling, she kept on growing, but not all of her grew at the same pace. Her skull ballooned in size, and her bones distended, bent, and finally popped out of her torn flesh. After exploding concussively from her chest, her ribs became a weird, arching pair of mountain ranges that encircled the layer like a looming cage. Meanwhile, her head bones continued to mushroom until they reached the size of a vast fortress.

Clearly, some force was using the Hag Countess's own body as the foundation for a new, utterly different kind of terrain. When the slope of Malbolge buckled, shifted, and found a new level, the Hag Countess's innards were buried beneath it, forming a twisting maze of subterranean passageways. Her organs burst to the surface as lakes of bile and viscera, and her fingers became white towers. Each strand of her coarse gray hair converted itself into a greasy, hellish tree, and her teeth sank into the earth, later to be mined as an inexhaustible source of ivory.

Through it all, the Hag Countess screamed and screamed. Even after her death should have been a certainty, her tortured cries kept echoing throughout Malbolge.

When the convulsions of the land began to wane and the Hag Countess's cries at last faded away, the layer's surviving inhabitants began to claw their way free of their earthen tombs and climb precariously from the layer's newly grown mountains. As they blinked in surprise at the new landscape, a golden litter floated up from the layers below. Winged devils held it aloft on straining shoulders, and snake-headed imps capered on its canopy. Lounging on silken pillows was the new ruler of Malbolge—Glasya, the cruel, beautiful daughter of Asmodeus.

When the Hag Countess's chancellor, a paeliryon named Axacrusis, dared to challenge the newcomer's presence, Glasya sashayed insouciantly from her litter and unfurled the letter of authority from her father investing her as Archduchess of Malbolge. She then demanded that Axacrusis eviscerate itself and invited her imps and bearers to feast on the remains. Axacrusis has yet to die, and Glasya's followers dine on the former chancellor still.

Since its dramatic change in leadership, Malbolge has become the layer of corrupt and bloated growth. Those who die on its cancerous ground are absorbed into it. Malbolge nourishes itself on these corpses, taking what it wants and leaving the rest as desiccated remnants to linger on in undying agony.