OSR Commentary Adapting I2: Dwellers In The Forbidden City by David Cook To The Barrows & Borderlands Rpg

 Adapting David Cook’s 1981 classic I2: Dwellers of the Forbidden City for a modern, grit-forward system like Barrows & Borderlands (B&B) requires shifting the focus from "heroic monster-slaying" to "tactical survival and factional maneuvering." This blog post picks right up from 

OSR Commentary Adapting C1: The Hidden Shrine of Tamoachan To The Barrows & Borderlands Rpg

The Forbidden City is essentially a "megadungeon" turned inside out. Here is how to translate its pulpy, lost-world atmosphere into the mechanical rigors of B&B.

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1. The Core Atmosphere: Decay & Resource Scarcity

In B&B, inventory slots and light sources are life. The Forbidden City shouldn't just be "hidden"—it should be a resource sink.

• The Jungle Trek: Treat the journey to the city as a series of Navigation Checks. Failure doesn't just mean getting lost; it means losing Rations or taking Fatigue levels before even reaching the gates.

• Verticality: The city is a massive crater. Use B&B’s climbing and encumbrance rules to make descending into the city a literal "point of no return."

2. Faction Warfare (The Social Engine)

The strength of I2 is the three-way war between the Bugbears, Mongrelfolk, and Yuan-ti. In B&B, combat is deadly, so players should be encouraged to use the Reaction Table.

Faction	B&B Archetype	Disposition	Hook
Mongrelfolk	Scavengers / Outcasts	Skittish	Will trade secrets for "pure" food or scrap metal.
Bugbears	Heavy Infantry	Aggressive	Looking for "conscripts" (meat shields) for their next raid.
Yuan-ti	Eldritch Cultists	Manipulative	Will offer "blessings" (mutations) in exchange for live sacrifices.

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3. Mechanical Conversions

B&B usually scales lower than AD&D. To keep the "Forbidden" feel, monsters should be dangerous but predictable in their behaviors.

The Yuan-ti (The Apex Predators)

Don't just give them high HP. Give them Special Abilities that interact with B&B’s conditions:

• Hypnotic Gaze: Target must make a Will Save or be Stunned for 1 round.

• Toxic Blood: If a Yuan-ti takes Slashing damage, adjacent players must check vs. Poison or take 1d4 damage.

The Tasloi (The Nuisance)

These should be B&B "Minions." They don't do much damage, but they excel at Stealing Items. Have them target a player’s "Utility Slot" (potions, torches) rather than their HP.

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4. Hazard & Exploration Tweaks

The environment is as much an enemy as the inhabitants.

• The Great Swamp: Movement is halved. Any roll of a "Natural 1" on an attack or dodge results in being Mired (requires a Strength check to move).

• The Horrors in the Pits: Use the Ablative Armor rules for creatures like the Aboleth or Pan Lung (the oriental dragon). Players shouldn't be able to "swing" their way through these; they need to find environmental weaknesses.

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5. Loot & Treasure

B&B focuses on "Wealth vs. Weight."

• The Yuan-ti Hoard: Instead of just "1,000 gold," describe it as Heavy Golden Idols. They are worth a fortune but take up 3 slots each and impose a penalty on Stealth checks due to clinking.

• Ancient Tech: Treat any found magic items as Relics with limited charges. Once they're gone, the item becomes a "Curiosity" worth gold but no longer functional.

GM Tip: The "Forbidden City" functions best when the players feel like they are caught in a pressure cooker. Keep track of Time Turns. Every hour spent debating is another chance for a rival faction's hunting party to find them.

  

Since you’re leaning into the lethality, we need to ensure the climax at the Temple of the Yuan-ti feels like a "survival horror" event rather than a fair fight. In Barrows & Borderlands, a lethal boss isn't just a bag of hit points; it’s a force of nature that requires the players to sacrifice resources or limbs to survive.

Here is how to tune the final encounter for maximum tension.

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The "Final Boss": The Yuan-ti Abomination

In the original module, this is often a high-level priest. For a lethal B&B conversion, we’ll treat it as a Lesser Horror.

Stats & Dread Logic

• Aura of Cold Blood: Any PC starting their turn within 10ft must pass a Will Save or take a penalty to their next Attack roll as their lizard-brain triggers a freeze response.

• Multi-Attack: The Abomination attacks twice: once with a Scimitar (1d8+2) and once with a Constrict (see below).

The "Constrict" Mechanic (The Death Spiral)

If the Abomination hits with its tail, the player is Grappled.

• Automatic Damage: The player takes 1d6 crushing damage at the start of every turn.

• Resource Loss: To represent the ribs cracking, the player must choose: take an extra 1d6 damage OR permanently destroy one item in their Inventory Slots (shield shatters, potion vials break, etc.).

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Environmental Hazards: The Sacrificial Pit

The fight shouldn't take place on a flat floor. The Temple is crumbling.

• Slippery Blood/Oil: The floor around the altar is "Difficult Terrain." Any Dash action requires a Dexterity Check or the player falls Prone, granting the Yuan-ti Advantage on its next strike.

• The Snaking Pillars: The Abomination can use its move action to vanish into the rafters. If the players lose sight of it, the next attack is a Surprise Attack (likely targeting the character with the lowest Armor).

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The "Hard Choice" Victory

To make it feel like an authentic old-school module, give the players a way to win that doesn't involve "bonking it until it dies," but comes at a high cost:

The Sacrifice	The Mechanical Result
Topple the Great Idol	Requires 2 players to spend their full turn. Crushes the boss for massive damage but collapses the exit, forcing a dangerous escape through the "Unexplored Tunnels."
Ignite the Swamp Gas	If players have a torch, they can ignite the vents. Deals 3d6 AOE damage to everyone. The boss dies, but players must check for Permanent Scars/Burns.
Offer a Blood Debt	A player can "Accept the Mark." The boss stops attacking, but that player now has a Yuan-ti Taint, suffering a permanent penalty to Charisma and a future plot hook.

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Implementation Advice

Note: Do not hide the lethality. Describe the "piles of bleached adventurer bones" and the "unnatural speed" of the creature. In B&B, players should only engage in a lethal boss fight if they’ve failed to find a clever way to bypass it—or if they are desperate for the loot.

OSR Commentary Adapting C1: The Hidden Shrine of Tamoachan To The Barrows & Borderlands Rpg

 

Adapting the classic C1: The Hidden Shrine of Tamoachan to the Barrows & Borderlands (B&B) framework requires shifting the focus from standard dungeon crawling to a high-stakes, survival-horror "extraction" crawl. This blog post picks right up from Adapting X2 Castle Amber (Chateau d' Amberville) By Tom Moldvay For Barrows & Borderlands Rpg

In B&B, the primary antagonist isn't just the monsters—it’s the Poisonous Gas and the ticking clock of your party’s resources.

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### The Core Hook: The Suffocation Mechanic

In B&B, environmental hazards are lethal. As soon as the players fall into the ruins, they are affected by the Miasma of the Sunless Shrine.

• The Clock: Every 10 minutes (one Dungeon Turn) of exploration, players must tick off 1 Ration or Torch to represent the extra effort of breathing/moving through the thick dust.

• The Penalty: If the party stops for a Long Rest, every character must make a Vigor Save. On a failure, they gain the Fatigued condition, reducing their maximum Grit until they reach fresh air.

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### Converting Key Encounters

Barrows & Borderlands thrives on "Weird Fantasy" tropes. Here is how to reskin the iconic Tamoachan threats:

Original Element	B&B Adaptation	Mechanical Twist
The Giant Slug	The Slime-Crusted Horror	Acts as a "Terrain Hazard." Its trail forces an Agility Save or the character is Stuck.
The Vampire (Zotzilaha)	The Hemomancer Wraith	Instead of level drain, it drains Grit directly. If Grit hits 0, the player becomes a Thrall.
The Doppelganger	The Echo-Shifter	It doesn't just look like a PC; it copies the last Ability the PC used against it.
The Gas Traps	The Blight Vents	These deal direct Inventory Damage. Instead of HP, the gas rots 1d4 random items in the backpack.

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### The "Borderlands" Twist: Loot and Relics

Since B&B emphasizes the value of "The Haul," the Olman treasures should be more than just gold.

• The Mirror of Itzpapalotl: In B&B, this acts as a cursed focus. It allows a caster to double their spell range, but every use requires a Sanity Check.

• The Jade Mask: This functions as a "High-Tier Helm." It grants immunity to the shrine's poisonous gas but prevents the wearer from speaking or casting spells with verbal components.

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### Navigation & Hazard Levels

To maintain the B&B "Meatgrinder" feel, divide the shrine into three distinct Hazard Zones:

1. The Lower Chambers (The Crawl): Focus on Vigor and Agility. Heavy on pit traps and collapsing ceilings.

2. The Middle Tier (The Ritual): Focus on Wits and Lore. This is where the environmental puzzles and "The Centaur" reside.

3. The Upper Tier (The Breach): Focus on Combat and Speed. The gas is thickest here; players must find the exit before their Gear Slots are depleted by rot and exhaustion.

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Design Note: Use the B&B Reaction Table for the various guardians (like the Giant Crayfish). Not everything in Tamoachan wants to kill the players immediately; some might be willing to trade "Safe Air" locations for the party’s precious supplies.

Gemini said

In Barrows & Borderlands, guardians aren't just bags of hit points; they are atmospheric hurdles that test a party’s resources, sanity, and tactical positioning. To fit the "Borderlands" feel, these Olman guardians should feel like ancient, semi-sentient bio-mechanical or spirit-bound constructs.

Here are the primary guardians of Tamoachan adapted with B&B mechanics:

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### 1. The Teotl-Amoxtli (The Tome Guardian)

Originally a giant crayfish, in the B&B version, this is a massive, chitinous horror fused with obsidian shards, guarding the sunken bridge.

• Hazard Level: High (Physical)

• Key Attribute: Armor 4 (Obsidian Shell).

• The Threat: Its claws don't just deal damage; they have the Sunder quality. On a successful hit, the player must sacrifice 1 Defense Item (Shield or Armor) or take double Grit damage.

• The Twist: It is bioluminescent. If killed, its internal fluids can be harvested to create 3 Durable Torches that burn underwater and in gas.

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### 2. The Zotzilaha Vampire (The Bat God’s Avatar)

Instead of a traditional vampire, this is a desiccated, leathery humanoid suspended in a glass vat of preservative "God-Blood."

• Hazard Level: Extreme (Supernatural)

• The Draining Gaze: Anyone making eye contact must pass a Spirit Save. Failure results in the Weakened condition—all Physical checks are at a disadvantage until the player consumes a full Ration.

• Echo-Flight: It does not walk; it blurs between locations. Melee attacks against it suffer a -2 penalty unless the room is illuminated by more than one light source.

• The Loot: The Heart of Zotzilaha. Can be crushed to instantly restore all Grit to the party, but inflicts a Permanent Scaring on the user's soul.

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### 3. The Nahual (The Jaguar-Man)

The classic shapeshifter of the shrine, re-imagined as a "Shadow-Stalker" that haunts the party through the ventilation shafts.

• Hazard Level: Medium (Stealth/Ambush)

• Stalking Mechanic: The Nahual does not attack head-on. Every time the party rolls a "1" on an Exploration check, the Nahual strikes the person at the back of the marching order and vanishes.

• Prowess: It ignores the first 2 points of damage from non-silvered weapons.

• Weakness: It is terrified of True Fire. A torch held high keeps it at bay, but using a torch in the gas-filled lower levels risks an explosion.

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### 4. The Kulkulkan Construct (The Feathered Sentinel)

A mechanical serpent made of gold, jade, and feathered silk, coiled around the central pillar of the upper tiers.

• Hazard Level: High (Environmental)

• The Coiling Constriction: Instead of biting, it wraps around a target. The target is Restrained and loses 1d6 Grit per turn from crushing force.

• Jade Scales: The construct is immune to Poison and Bleed effects.

• Tactical Solution: The construct is powered by a large gemstone in its forehead. A character can attempt a Wits Check to jam the mechanism with a crowbar or tool, bypassing the fight entirely.

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### Guardian Stat Block Template (B&B Style)

Guardian	Grit	Saves (V/A/W/S)	Special Ability
Obsidian Horror	22	15 / 8 / 5 / 10	Sunder: Destroys gear on a Crit.
Bat Avatar	18	8 / 14 / 16 / 15	Lifesteal: Heals 1d4 on hit.
Shadow Jaguar	12	10 / 18 / 12 / 8	Vanish: Disappears after attacking.
Jade Serpent	25	16 / 12 / 8 / 5	Heavy: Cannot be pushed or tripped.

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### Management of "The Haul"

In B&B, these guardians are often standing on top of Relics. When a guardian is defeated, roll on the Ancient Olman Loot Table:

1. Macuahuitl of Woe: A wooden sword embedded with obsidian. Deals +2 damage but breaks (is removed from inventory) on a natural 1.

2. Chacmool Basin: A stone bowl that purifies any liquid placed inside, turning it into Clean Water (1 Usage).

3. Quetzal Cloak: Grants the wearer a +4 bonus to Agility Saves involving jumping or falling.

Legacies In Sand - C1 "The Hidden Shrine of Tamoachan" (1980), by Harold Johnson and Jeff R. Leason & I1: "Dwellers of the Forbidden City" (1981), by David "Zeb" Cook

The Hidden Shrine draws from a caricature of Aztec and Mayan culture, just as traditional D&D draws from a caricature of the European middle ages. In a retrospective, James Maliszewski wrote, “The Mesoamerican flavor gives the whole thing an ambiance quite unlike other D&D modules. The whole thing has an ‘alien,’ exotic quality to it, which I think adds greatly to its appeal.”

So my campaign is set in a twisted Castles & Crusades/Victorious rpg   1870's during the Franco Prussian war  but one of the first places that my plane jumping version of Tegel Manor is visiting is Mexico for the first leg of the campaign.


Now this isn't an accident. The reason for this is that deep in the jungle swamps of Mexico is a lost valley gate way leading to C1 "The Hidden Shrine of Tamoachan" (1980), by Harold Johnson and Jeff R. Leason.




Originally in my game the shrine belonged to  the quinametzin a race of giants found in 

Mesoamerican mythology. These giants are not gone but now a race of undead lich kings inhabiting certain forgotten demi planar valleys that dot along certain areas of Mexico. Their very active within the affairs of their own demi planes snatching explorers & the occasional adventurers from other worlds.
What's the connection to Tegel Manor?! Several artifacts belonging to the quinametzin are now among the Manor's collections of relics & artifacts. These were stolen by the Rumps & the giants want them back! There's been talk among fellow DM's that I should connect up G1 -3 Against the Giants By Gary Gygax  with this on going  campaign. Personally I think its a bit much at this point. I1 "The Hidden Shrine of Tamoachan" (1980), by Harold Johnson and Jeff R. Leason fits the 'Lost World' vibe that I'm going with for this war torn otherworldly campaign.




Instead I'm looking into possibly using  I1: "Dwellers of the Forbidden City" (1981), by David "Zeb" Cook in conjunction with  "The Hidden Shrine of Tamoachan" (1980), by Harold Johnson and Jeff R. Leason. I've done this for Astonishing Swordsmen & Sorcerers of Hyperborea in the past. But this time I'm weaving in the undead pulpy legacy of  the quinametzin kings into the mix.


I've already got the better part of a year's worth of campaign material already crammed into note books. But this is where Venger Satanis's  Cha'alt the interloper comes in. Rival adventurering parties from Cha'alt are already in the mix here. They'll be getting through the trips & traps of Mexico's adventure locations, supplying arms & armament, & causing my player's adventurers all kinds of mayhem! 

Several forces of Cha'alt loath the adventurers & have a couple of mecha waiting to take the party just outside the hidden valley's of the the quinametzin! There will be blood coming up! But whose remains to be seen!