Door is closed, and warded against damage and unlock spells. Depicts a bunch of snakes worshipping at a pyramid. Sunburst on top of pyramid.

Inscription in proto-yuan-ti reads: "The Golden Disc will light the way."

A "keyhole" of sorts seems to want to accept a large, coin-shaped object with a complex embossing of a snake god.

As a reward for entering, the party is immediately attacked. A cloud of poison immediately pours forth from the door. The poison causes 1d6 Con damage ots (Fort negates); each breath adds another stack. Assuming one doesn't breathe, 3 consecutive successes can clear the poison (but not cure the damage).

Once past the poison, they can see the room. It's big and square, with a sunken platform at the center. The walls are lined with yuan-ti statues offering organs and bits of things as if in sacrifice to gods.

The inner pit is filled with hundreds (thousands?) of black snakes, writhing over each other. They seem to be in a constant cycle of feeding and sleeping. Beneath the center of the pile is...something...

Gotta kill all the shadow asps to unlock the elite. Gotta kill him to move on.

Shadow Asp

There are 10 swarms of shadow asps:

• Large minion (swarm)
• Incorporeal
• Immune to shadow, vulnerable to holy
• Swarm attack: shadow damage, poison, negative energy

Tortured Couatl

An undead couatl; its body is visible as a translucent form, constantly regenerating from the asp bites; its skeleton seems real enough.

• Huge undead beast
• Controller 11 (elite)
• Should have like 20M hp or something
• Undead (positive energy)
• Seven Veils: series of powerful defenses (90% res to various things) that need to be taken down in a special way; after that, he's easy to kill
• Attacks: prismatic rays, holy priest attack spells (complete with RF)
• Defenses: priest defense spells (bubble, heals)

After killing the couatl, it asks you to destroy its skeleton and put it to rest. Yields the Serpent Stone, needed to progress.

The way out is some sort of complex, interlocking door mechanism.

Four stone snakes coil together to lock the door in place. Each leads to one of the four corners of the room, where the snake's tail forms a lever. At the center of the heads is a slot for the serpent stone.

Marked on the Serpent Stone are dashes indicating numbers: 3 7 11 13

Near each tail is an inscription in yuan-ti:

• Lower left: 1
• Upper left: 10
• Upper right: 11
• Lower right: 100

Solution:

• First, insert the serpent stone.
• Input the correct sequence: 3, 7, 11, 13
• How to input: the levers represent binary digits. The first digit is the lower left (1), second is upper left (10, aka 2), etc. To input 3, which is 11 in binary, activate both left tails and no right tails, then press the serpent stone in. As soon as this is done, one snake head retreats and the tails reset. If the next number is right, the next head retreats, etc; if the stone is pressed when the levers aren't right, the most recent head resets.
• When all four numbers are entered, the door opens.