d12 Hauntings in the Dungeon of Zenopus

Detail from a Clarkson Stanfield illustration

"...but then neighbors and the night watchmen complained that ghostly blue lights appeared in the windows at night, that ghastly screams could be heard emanating from the tower at all hours, and goblin figures could be seen dancing on the tower roof in the moonlight". 

As told in the introduction to the Sample Dungeon, after the demise of Zenopus his tower was haunted by mysterious forces until it was destroyed by the town. While this stopped the above ground hauntings, it seems likely they would continue in the passages beneath. To this end, here I've written out 12 possible  hauntings that may visit a party exploring the dungeon. You might add a chance of one appearing when making a wandering monster check (e.g., a 1 on the d6 is a standard wandering monster, while a 2 is instead a haunting). The ones marked with a star should only appear once.

1*. An insane antiquarian (DX 10, AC 5, HD 0, hp 2, #AT 1 fists for 1 point) wearing an octopoid crown rushes the party, yelling for submission to the eight-armed sea queen, and pummeling whoever is closest. The antiquarian will (temporarily?) regain sanity if the crown is removed and they are brought out of the dungeon. The crown was found in an ancient chamber discovered when a cellar was excavated in Portown, and cannot be removed once worn (treat as a cursed ring of protection +2 that slowly drives the wearer mad).

2. A column of sickly green flame, 5' wide and 10' high, spouts from the floor (1-3 = ahead 10-100', 4-5 = behind, 6 = directly under party). All viewing it feel increasingly queasy (save versus spells each round or flee for 1d6 rounds). If touched or hit, the cold flame suddenly leaps on to the attacker and burns away vital forces (one point of Constitution per round; make a new save to break away). Once Con is exhausted, the victim's flesh withers, leaving an animated skeleton wearing their equipment. For survivors, Con is regained at the same rate. The column burns for 1d6 rounds after last touched. 

From the HP Lovecraft wiki

3*. An old skeleton (DX 6, AC 6, HD 1/8, hp 2, #AT 1 touch with green fire) wearing tattered blue robes totters unsteadily down the corridor. A cold green flame burns in its eye sockets. It feebly attempts to grab anyone approaching within 20 feet (the limit of its "sight"). If touched or hit, the green flame reacts as in #2 above. If the skeleton is destroyed the fire burns for 1d6 rounds. It wears a gold ring with an italicized "Z", value 50 gp. This is a former servant of Zenopus slain when the green flame engulfed the tower fifty years prior.

4. A ghostly blue light illuminates the corridor, slowly coalescing into a shape vaguely like a blue-robed figure. If the party lingers, the character with the highest Intelligence must save versus spells. If they save, the spirit will assault the next most intelligent character, and so forth. Failure results in a whispering in the mind urging the character to spend the night in the dungeon (save again to leave). Each night in the dungeon temporarily drains a point of Wisdom, until zero when they are under control of the spirit, which is that of a sinister wizard from the past, wishing to return to life (optionally, this is Zenopus himself).

Cover art for "L'Affaire Charles Dexter Ward"

5. A lone ghastly scream is suddenly heard in the distance, but the direction is not clear, and it is not immediately repeated. Roll again for a chance of a wandering monster.

6. A shadowy goblin-sized figure (DX 18, AC 2, HD 1, hp 5, #AT 1 claws for 1d6) hangs from a wall at the edge of the party's light source. It hisses and dances away if the light advances. This is one of many small otherworldly familiars summoned by Zenopus to aid in his laboratory, and now trapped in our world. If a magic-user approaches alone and converses with the creature it may agree to serve as a familiar (make a reaction roll).

From "A Special Trick" by Mercer Mayer

7*. An armored zombie (DX 8, AC 5, HD 2, hp 8, #AT 1 claws every other round for 1d8) begins following the party. It does not attack unless attacked itself. An unsuccessful adventurer, it seeks the way back to town. It wears chainmail, a helmet and a leather backpack, which holds equipment and a note from one Griselda of Portown, dated months ago. If destroyed and the body returned to Griselda she will reward the party with 100 GP. If the party does not destroy the zombie, it will follow them out and return to her on its own.

8. A salty sea fog rolls across the floor and begins to fill the corridor or room. Each round it grows 1 foot higher, continuing no matter how far the party travels during this time, until it reaches the ceiling. Once, this occurs visibility is reduced to 1 foot (and all attacks are made at -2). After 1d6 turns, the mist will dissipate. 

9. A wind of fine sand picks up, gentle at first but but increasing in speed and particle size to a hail of pebbles and then a gale of rocks. All torches are extinguished in 1d6 rounds, and all who stay in place may take damage (roll an attack by 5 HD monster for 1d6 damage each round) before it subsides (2d6 rounds). The wind can be avoided by finding cover or going around a corner, as it only blows in a straight line.

10*. A ghostly crabber stalks the party from fifty feet behind; loud wet footsteps are heard. The ghost is covered in sucker marks and kelp (a victim the pirates fed to the giant octopus). If the party halts it stops and wordlessly points in the direction of the pirates (Cave M). If approached, it vanishes and reappears behind them. This keeps up until vengeance against the pirates is achieved, when it fades away, leaving a golden crab worth 1,000 gp.

Ghost of a Drowned Fisherman by Michael Wandelmeier

11*. The shadow of each character begins to divide, forming a second one doubling the first. Each turn there is a 1 in 6 chance of noticing this; after 1d6 turns the shadows detach and attack the respective characters (if unnoticed, surprise is on 1-3 in 6). Each character fights their own shadow (AC 9, HD 1, hp equal to character, #AT 1 shadow weapon for 1d4). Extinguishing all light will delay the progression for an equal amount of time. 

12*. The enormous bloated corpse of a former Portown bon vivant and charlatan slowly shuffles towards the party. It smells terrible, and mutters in a strange multi-voiced manner. It is not undead, but is instead animated from within by larvae (human-headed hellworms; see the Monster Manual for a description). If struck by any weapon it explodes in a shower of swamp gas (save vs poison or attack at -2) and larvae (2d4 total; AC 7, HD 1, hp 5, #AT 1 bite for 1d4+1), which surprise on 1-4 in 6. Hidden in the intestines of the corpse is a stolen blue diamond worth 500 GP, which caused their death when swallowed to hide the evidence.

Larvae by David C. Sutherland III