The Corrupted Volcano — The Living Mountain

Gargantuan aberration (far realm infection), chaotic evil

The Fire Giants’ Hall is not just a volcano. It is a living entity — infected by the same Far Realm corruption that makes Allabar what it is. The mountain was hollowed out by the giants, but the Far Realm grew into the wounds. The walls breathe. The stone pulses. The lava flows where the mountain wants it to flow.

Vecna channels through this connection. The volcano is his relay — its corruption network links to every possessed giant, to the dragon’s tethers, to the slaad tadpoles, to Allabar itself. The mountain is the antenna. Vecna is the signal.

The dragon was the first victim. The fleshy Far Realm tethers that bind the ancient white dragon to the wall aren’t chains — they’re the volcano feeding on it. Draining it. The dragon’s life force powers the corruption network. When the tethers are severed, the volcano feels it.

The meteorite destroys it. The star fragment called down by the giants’ ritual will hit the anvil — but the impact shatters the mountain. The corrupted volcano dies. The tether network collapses. Every possessed giant drops. This is the necessary sacrifice: to forge the weapon, the mountain must fall.

The Volcano Is the Encounter

The Corrupted Volcano doesn’t have a position on the map. It IS the map. The walls, the floor, the ceiling — the corruption is woven through all of it. It attacks through necrotic Far Realm tethers — fleshy, veined tentacles that erupt from the walls, the floor cracks, and the lava vents. They reach for the party the same way they hold the dragon.

Vecna directs the tentacles. When Vecna wants to disrupt a station operator, corrupt the forging sequence, or punish someone who refused his bargain — the walls attack.

Stat Block — The Corrupted Volcano

The volcano doesn’t take turns in initiative. It uses Lair Actions on initiative count 20 (losing ties) and Legendary Actions between turns.

Armour Class — (the volcano itself can’t be targeted; individual tethers can)
Hit Points — The volcano has no HP pool. It dies when the meteorite hits. Individual tethers have 30 HP each, AC 12, and are vulnerable to radiant damage.
Damage Immunities fire, poison, psychic
Condition Immunities all

Tether Properties

Each tether tentacle that erupts from the walls:

• AC 12
• HP 30
• Vulnerability radiant damage
• Immunity fire, poison, psychic
• Reach 30 ft. from the wall it emerges from
• If severed (reduced to 0 HP), the tether retracts. A new one can emerge from a different wall section on the next lair action.
• Regeneration: Unsevered tethers regain 5 HP at the start of each round.

Lair Actions (Initiative Count 20)

On initiative count 20, the Corrupted Volcano takes one of the following lair actions. It cannot use the same one two rounds in a row:

1. Grasping Tethers. 1d4 fleshy tentacles erupt from the walls or floor cracks within 30 ft. of the forge island edge. Each targets a different creature. Melee Attack: +8 to hit, reach 30 ft. Hit: 11 (2d10) necrotic damage and the target is grappled (escape DC 16). A grappled creature takes 5 (1d10) necrotic damage at the start of each of its turns. The tether drags the creature 10 ft. toward the nearest wall on each of the volcano’s lair actions unless the creature escapes or the tether is severed.

2. Corruption Pulse. The veins in the walls pulse sickly green. Each creature on the forge island must make a DC 15 CON save or take 7 (2d6) necrotic damage and have disadvantage on their next ability check (including station checks). On a success, half damage and no disadvantage. The forge itself shudders — steam vents misfire, gears slip.

3. Tether Surge — Station Disruption. The volcano targets one forge station specifically. A mass of tethers erupts beneath the station operator. The operator must make a DC 16 STR save or be pulled off the station (moved 10 ft. away) and knocked prone. On success, they hold position but take 5 (1d10) necrotic damage from the tethers clawing at their legs. Vecna directs this — he targets whichever station is most critical that round.

4. Far Realm Whisper. The corruption network hums. One creature of Vecna’s choice must make a DC 15 WIS save or be confused (as the confusion spell) until the end of their next turn. The creature hears Vecna’s voice overlapping with alien Far Realm static — words that almost make sense but belong to a geometry that shouldn’t exist. Use this when Vecna wants to reinforce a bargain — target whoever he was just whispering to.

Legendary Actions (2/Round)

The volcano can take 2 legendary actions, choosing from the options below. Only one legendary action can be used at a time, and only at the end of another creature’s turn.

Lash (1 Action). One existing tether makes an attack: +8 to hit, reach 30 ft., 11 (2d10) necrotic damage.

Drag (1 Action). One creature currently grappled by a tether is dragged 15 ft. toward the nearest wall. If they reach the wall, they are restrained (escape DC 16) as the tethers begin to cocoon them — the same process that bound the dragon.

Tremor (2 Actions). The forge island shakes. Each creature standing on the island must make a DC 14 DEX save or fall prone. Lava splashes over the edges — any creature within 5 ft. of the island edge takes 7 (2d6) fire damage. The mountain is angry.

How It Plays

The volcano is not a monster the party fights — it’s the environment fighting back. Vecna uses it to:

1. Pull operators off stations (Tether Surge) — works with the devil territory control. A tether yanks someone off, a devil takes the station.
2. Punish refusals — If someone rejects Vecna’s bargain, the walls attack them next round. Make it personal.
3. Drain the party — Corruption Pulse chips away at HP and imposes disadvantage on station checks. Attrition pressure.
4. Mirror the dragon — When tethers grapple a PC and start dragging them toward the wall, the party sees what happened to the dragon happening to THEM. Alora especially should feel this.
5. Escalate with the chanting — As the giants’ ritual intensifies, the lair actions get worse. Round 1-2: single tethers, gentle. Round 3-4: multiple tethers, Corruption Pulses. Round 5: Tremor + everything at once. The mountain knows what’s coming.

When the Meteorite Hits

The volcano screams. Not a sound — a vibration through the entire mountain. Every tether goes rigid, then limp. The veins in the walls stop pulsing. The corruption network dies. Every possessed giant above drops simultaneously — puppets with cut strings.

The mountain begins to collapse. The entity is dead. The relay is gone. For the first time in centuries, the volcano is just a volcano.

And it’s falling apart.

Interaction with Other Encounters

• The Dragon: The dragon’s tethers are the oldest and thickest. Severing them (STR DC 18 or radiant damage) doesn’t just free the dragon — it hurts the volcano. Each dragon tether severed reduces the volcano’s lair action attack bonus by 1 (from +8 to +7 to +6). Three tethers on the dragon. Free the dragon = weaken the mountain.
• Lux’s Grip Checks: The tether network IS the network Lux’s body responds to. When the volcano uses Corruption Pulse, Lux has disadvantage on his next Grip Check if he fails the CON save. The body and the mountain are part of the same system.
• Jesse’s Aura of Hate: Jesse’s aura doesn’t buff the tethers (they’re aberration, not undead/fiend). But if Jesse stands near the north wall (portal 3), the tethers in that area become more aggressive — Vecna focuses his attention where his champion stands.
• Alora: If Alora casts radiant damage spells near the walls, tethers in a 15 ft. radius retract and don’t re-emerge for 1 round. Sacred Flame, Guiding Bolt, Spirit Guardians — the Far Realm corruption can’t tolerate radiant energy. This gives Alora a dual role: healer AND environmental control.