How does Ragnarök start? Does it commence as a natural catastrophe? As some inevitable shifting of the universe toward destruction? No. Instead its arrival is heralded by pride, greed, and that deepest of all sins — an unquenchable lust for power.
Ragnarök’s first trigger is the desire of Surtur, King of the Fire Giants, who dreams of conquest in the flaming land of Muspell. It starts as his protégé — the Duergar liege Doomshallow — digs ever deeper for ores and treasure to fund Surtur’s never-ending wars. It commences in the fiery mountain fortress of Soria, that sits on a deep, dark, poison-filled mine.

There Doomshallow’s enslaved miners delve into Svartalfheim’s bowels. They unearth a dark, oily liquid as their picks and tools cleave the rock. They’ve tunneled down, down to pierce the very black Lake of the Dead in Niflheim. Its waters, which hold the dead’s spirits, leak into Soria’s mines. Infused with the power of death, their toxic flood transforms Soria’s slave miners into hordes of zombies, skeletons, shadows. Doomshallow at first battles these undead. But soon he learns to enthrall them, to bind them into a horde of diggers that never grow weary. He uses this slave force to construct serpentine pumps that snake down into Soria’s pits. The pumps themselves are powered by the deathly energy running through the liquids they suck up. He stores the oily fluids of Lake Niflheim in great vats. He uses the liquids to swell the ranks of his miners, his armies. To power his machine pumps. He sells the fluids to the Fire Giants of Surtur who learn to forge mighty weapons out of their deathly secretions.
Hel, Queen of the Dead, in her palace on the shores of Lake Niflheim, hears rumor of Doomshallow’s mines, of Surtur’s lust for conquest. Seeing the great wealth flowing into Soria from Muspell, she grows jealous. She has always desired the Fire Giants’ gleaming red gems. It is unfair, she thinks, that Doomshallow should gain them all. She sends out her spies. They tell her Surtur seeks weapons of war. Now that she knows what the Fire Giants want, she can devise a way to snatch up their gems. She sends a message to Surtur. She tells him that the great chain of Fenris lays embedded in the deeper rocks of Soria. That its metals can be forged into a mighty weapon for his conquering armies. It only need be mined. This chain is strong, she says. It has held Fenris for ages and ages, she assures. Just a few of its metals will not weaken it enough to break, she cajoles. She proposes to work with Doomshallow to forge the weapon. She has cunning plans for its design. Pointing at the serpentine pumps in Doomshallow’s mines — she says “That is the shape it shall take.”
Surtur’s eyes glitter at Hel’s words. Doomshallow hears them and only thinks of further profit. A pact between the three is formed. Fenris’s chain shall be mined. A great weapon shall be forged from the metals of its links.
So Doomshallow mines, Surtur forges weapons, Hel plots. They all grow rich. The liquids flowing from Lake Niflheim swell from a trickle into a flood. Their fluids are used for slaves, for weapons, for serpentine pumps. The chain of Fenris is tapped. Its powerful metals removed. Hel, Surtur, and Doomshallow begin to forge a great serpent war machine.
Deep in Yggdrasil’s longest root as it winds down toward the land of Hel there lives the great dragon Nidhogg. Here he lairs on the shores of Lake Niflheim. Within the lake’s oily liquids the dead are dissolved. Nidhogg drinks of this lake. He thus devours the dead. In this way his raging hungers are satisfied. Now with Doomshallow’s pumps and with Surtur’s hungry forges the lake’s levels are running low. Nidhogg grows ravenous. He says to himself “The waters of the dead are not longer so thick and satisfying. I will also eat this root of Yggdrasil to slake my hunger.”
So Nidhogg turns his maw to devour great Yggdrasil. The root reacts by spawning a swarm of smaller roots that burst forth. They plunge into Lake Niflheim. They swarm up through the void of Ginnungagap. They carry with them the dark fluids of the lake. The undead ride their courses. They grow up to entangle Svartalfheim and Midgard. Ripping through their lands and carrying the dead with them. As they grow they take more fluid from Lake Niflheim. So Nidhogg‘s hunger swells. His devouring of Yggdrasil quickens.

At last Surtur’s weapon is nearly constructed. It is made of an alloy forged from Fenris’s chain. The metals that Doomshallow’s zombie slaves mined now form its great spine. It is a monster machine fed by the liquids of Lake Niflheim — burned in the fires of its strangely beating heart. The spirits of the dead scream as they burn — animating it with unnatural life. A massive draconic serpent spewing poisons. Surtur names it after the first land he intends to conquer — Midgard.
As the last plate in the Midgard Serpent is forged, the chain binding Fenris Wolf shatters. The great wolf is freed at last. He arises, swells through Ginnungagap, begins to stretch his jaws across the skies. His long captivity ignites great hunger. He gapes to devour sun, moon, and stars. A fore-sign of Fimbul Winter. As Fenris slavers for his celestial dinner, Yggdrasil roots grow up into Midgard. They rip a hole at the base of Lake Mimisbrunnr. Odin’s Eye, long dormant in the lake, falls through the hole and out into Ginnugagap. Thus freed from the waters it awakens and opens. It shines upward toward Surtur’s empire of Muspell. It reveals the jaws of Fenris closing on the sky.
All in Midgard see it. Unknowing, they behold the beginning of Ragnarök.
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The above description provides the Game Master with background events for The Deep Dark of Svartalfheim series of D&D modules in the Battlestorm Ragnarök campaign setting. Specifically, this background is a supplement to Troubles Rise from Yggdrasil’s Roots Part 1 and Part 2.