Vault 73-B: The Mimic Vault

Location: Kigum (The Grand Arcane Bank) Level Range: 7-8

"Precision is the soul of security, but even the finest gears can be choked by weeds. Do not trust the floorboards, and for the love of the Great Cog, do not trust the air you breathe." — Overseer Elara Brass-Heart

Background & Objective

Deep within the subterranean strata of Kigum, beneath the brass-shod vaults of the Grand Arcane Bank, lies Vault 73-B. Originally designed as a high-security containment facility, it is governed by an ancient, malfunctioning reality-anchor array. This array was intended to punish greed by projecting an adaptive cognitive field that manifests "mimicry" responses to intruders, turning mundane objects into territorial constructs.

However, the integrity of this mechanical reality-field has been compromised. The Omnisporangium—the sentient fungal god of Aethervale—has sensed the stagnant Aether crystals powering the bank’s defense grid. In an act of "cosmic surgery," the Mycelium has woven its shimmering, bioluminescent hyphae into the vault’s malfunctioning clockwork circuitry. The vault is no longer just a prison for wealth; it is a parasitic feeding ground where the Mycelium hijacks the bank's mimic-projection protocols to gestate predatory, spore-mutated mimics. The bank requires a specialized team to clear the vault and retrieve a plain wooden bucket—a mundane object of immense political importance containing sensitive diplomatic documents regarding the Crystal Embargo.

Sight, Sound, and Smell

The air is a heavy cocktail of hissing steam, ozone, and the sweet, cloying scent of damp earth and rotting chanterelles. Shimmering, translucent glitches flicker across the walls, momentarily turning copper pipes into writhing tentacles. The rhythmic, metallic thrum of the bank’s gears is occasionally interrupted by a wet, squelching sound from beneath the floorboards.

Rumors & Whispers

True: The vault’s reality field is being fed by a direct tap into a Mycelial Thread, meaning the mimics here share a collective, hive-mind intelligence.
False: The documents inside the wooden bucket contain the secret location of the "Sleeping Dragons" First Brood. (In reality, they are merely trade agreements with the Sub-Terran Accord).

Markings

Scratched into the brass plating of the vault’s primary decompression chamber is a symbol of a gear being cracked open by a sprouting mushroom.

Translation: "The metal breathes here; the hunger is rooted deep."

Key NPC: Overseer Elara Brass-Heart

The lead security engineer for the Grand Arcane Bank, Elara is a woman of copper-toned skin and stiff Victorian posture, her left eye replaced by a magnifying Aether-lens.

"The bank does not fail. It merely... recalibrates. Now, go in there and stop my vault from eating the clientele."

Ideals & Flaws

Ideal: Order. Everything has a place, and every gear must turn in sequence to maintain the stability of Kigum.
Flaw: Denial. She refuses to admit that the bank’s technology is being effortlessly subverted by the "primitive" fungal intelligence of the Omnisporangium.

The Gimmick: Paranoia Induction

The vault's security system creates a localized field that makes inanimate objects appear as Mimics. Real Mimics, augmented by the Mycelium’s Blue Bile, are also present.

The Reality Anchor: Players must contend with "True Sight" or physical testing (hitting things) to navigate. However, the fungal hijacking adds a twist: the spores in the air cause hallucinations, making even "True Sight" occasionally flicker or show the "soul" of the objects as hungry, toothy maws.

Tactical Combat & Challenges

Mimic Colony Battle

The final chamber is a masterpiece of deceptive horror. The floor tiles are mimics (applying the Grappled condition), the heavy pneumatic door is a mimic, and the shimmering "treasure chest" in the center is a massive, mutated Spore-Mimic.

Tactics: The mimics in Vault 73-B act in concert. The "Floor Mimics" grapple players to keep them stationary while the "Ceiling Pipes" (also mimics) drop acidic Blue Bile from above. They target players who use fire or light first, as the Mycelium prefers the dark to spread its spores.
Ecology: These are not natural mimics; they are Litho-Mycelial symbiotes. They feed on the Aether-leakage from the reality anchor. By consuming the "stagnant" magic of the bank, they are effectively acting as a localized immune response, breaking down the artificial structures that the Omnisporangium deems parasitic to the world's equilibrium.

Deceptive Layout

The real objective—the wooden bucket—is the only object in the vault that is not a mimic or a projection. It is shielded by a lead-lined anti-magic field within its interior, making it invisible to the vault's hijacked sensors.

Narrative Outcomes & Loot

Success: The documents are retrieved, cooling the political tensions of the Crystal Embargo. The bank rewards the party with specialized storage items and 5,000 GP in assorted gems recovered from the "digestion" piles of neutralized mimics.
The Gilded Gastropod: A fist-sized, golden snail shell etched with rhythmic clockwork patterns.
- Mechanics: Acts as a Bag of Holding. Additionally, the user can blow into the shell to cast Leomund’s Tiny Hut once per week. The hut appears as a shimmering, iridescent shell.

Lore & Origin

The Gilded Gastropod was forged during the early days of the Steam Wrights Consortium. It was intended to be a portable bunker for surveyors exploring the deep Aether-veins. It is said the shell was tempered in Blue Bile, giving it a semi-sentient connection to the earth. It occasionally hums a low, rhythmic vibration when near a major Mycelial Thread, as if whispering to the world-organism below.