The Fane

An underground cathedral opens before you. At one end, a sculptured balcony perches atop five rearing stone serpents. Blood dribbling from the serpents’ jaws falls into a semicircular basin, and from there flows along a sloped trough into a wide stone bowl set into the floor. South of the bowl is a mezzanine, prominently situated atop which is a cauldron of steaming broth that exudes fleshy odors. To the west, a huge gong carved with snake patterns stands on a second balcony.

During rituals, the fane swells with yuan-ti, but the room is unguarded otherwise. When struck, the gong can be heard throughout the temple complex. One strike announces the start of a serpent ritual: when sounded, all the yuan-ti within the temple complex arrive here within half an hour. Two or more strikes in quick succession signal an alarm: when sounded, yuan-ti throughout the temple converge on this location as quickly as possible (see the Temple Roster table).
Blood Pool
Blood spilled in the Sacrificial Chamber is channeled into this room, and the central pool contains 3d6 inches of viscid, days-old blood from previous sacrifices. The yuan-ti wallow in the blood from time to time, and slaves are sometimes brought here to be eaten alive by crazed revelers or transformed into yuan-ti (see “Yuan-ti Rituals” below).
Cauldron
A stew made from boiled flesh sloshes inside the cauldron, which is heated by a volcanic vent in the floor underneath it. Upturning the cauldron is an action that requires a successful DC 15 Strength check. When the cauldron is tipped, each creature on the floor within a 15-foot cone of the cauldron must make a DC 12 Dexterity saving throw, taking 4 (1d8) fire damage on a failed save, or half as much damage on a successful one.
North Balcony and Teleporter
Ras Nsi and Fenthaza use the north balcony to address underlings. To climb up, a character must succeed on a DC 13 Strength (Athletics) check. The balustrades around the balcony provide half cover against ranged attacks originating from the room below.
Set into the back wall is an alcove with an engraved stone disk on the floor — one of Ras Nsi’s magic teleporters (see “Teleporters”).
Portcullis
A portcullis seals the entrance to the Harem. A bronze lever is set into the wall north of the gate, out of sight of the Harem. Lifting the lever raises the portcullis, and pulling the lever down causes the portcullis to drop.
Yuan-Ti Rituals
Once every ten days, the yuan-ti gather in the fane for a depraved ritual. The ceremony takes place over the course of one night, with a skeleton crew guarding the rest of the temple complex during these periods.
During the ritual, mesmerizing incense is burned in the wall sconces. (See area 13 for more information on the incense.) Fenthaza preaches to the congregation from the north balcony. As the ceremony reaches fever pitch, she joins the revelers in the blood pool to feast on the slaves before slithering back to her quarters. On occasion, human slaves are transformed into yuan-ti purebloods or broodguards during these rituals. To undergo the change, slaves must bathe with snakes in the blood of sacrificial victims while under the influence of temple drugs. The transformation leaves each slave with 1d6 levels of exhaustion. Once they’ve shed their old skin, those who survive the process are taken to their new home in the yuan-ti nests to recuperate. Those who die are fed to the hydra in the Hydra's Lair.
Fenthaza can arrange for captured human characters to be transformed into yuan-ti purebloods so they can roam freely within the temple complex and get closer to Ras Nsi. The transformation can be undone only by a wish spell or divine intervention. Characters who survive it gain a random form of indefinite madness. A human that undergoes and survives the ritual retains its traits and gains the following yuan-ti racial traits.
Darkvision. You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can’t discern color in darkness, only shades of gray.
Innate Spellcasting. You know the poison spray cantrip. You can cast animal friendship an unlimited number of times with this trait, but you can target only snakes with it. Starting at 3rd level, you can also cast suggestion with this trait. Once you cast it, you can’t do so again until you finish a long rest. Charisma is your spellcasting ability for these spells.
Magic Resistance. You have advantage on saving throws against spells and other magical effects.
Poison Immunity. You are immune to poison damage and the poisoned condition.
Navigation
The the north easten exit leads to the Throne Room, the Eastern exit leads to the Harem, the southern exit has multiple exits with the snake pit on the left, the venom distillery straight ahead, the Storeroom on the right then left, and then the Hall of Serpents on the the right straight ahead.