Three-dimensional movement has always been a challenge for Dungeon Masters and players. It’s something that logically occurs in aerial or aquatic environments, but also in environments like the Underdark. Caves evolve in any direction, despite the occurrence of them in a relatively two-dimensional sense in most adventures. Actual exploration of a cave system is a dangerous and sometimes difficult proposal, involving environmental risks and extra equipment and planning that don’t easily fit in a backpack. Accounting for this in a game setting isn’t always easy, although magic can account for a lot. Despite that, sojourns into the never ending night below are still some of the most treacherous.

Denizens of this place are adapted to this environment as one would expect. Superior vision for this setting is but the first adaptation. Those that burrow are common, as are those that swim through its watery places can climb over its rough surfaces. Climbing arthropods of all kinds flourish here. That’s not limited to insects.

One of these foes has been treated as an add-on for a very long time, and that includes by the culture it was spawned from. Driders are the product of drow elf society. As a spider version of a centaur-like being, they combine the advantages of both species, and would be an advance in the evolution of the species if it wasn’t a curse. A drider alone should be a great foe if played correctly, as they could easily snipe foes from any angle as they cling to high walls with their longbows. Sadly, they are rarely used this way.

That changes today. To make matters even more interesting, we’re going to take the drider, and then give it some extra love, so to speak. If a drider can already Web Walk, what happens when we give the drider access to the web spell? Not only will they be able to negotiate the walls and ceilings of a cavernous area, but the webs they create as well.

Underdark

6-7

Your party spills out into this large 50 ft. diameter roughly spherical cavern from the centre of the eastern wall. The floor slopes away to a bowl 25 ft. below you, mirroring how the ceiling rises above. The floor and ceiling are littered with smaller stalactites and stalagmites, rendering the terrain on the floor and ceiling into difficult terrain for horizontal movement. The top of the ceiling has an irregular ring of 5 ft. long stalactites dripping with white, calcium rich water. The very bottom of the floor has a small 5 ft. diameter pool ringed with white mushrooms.

Until the player characters make their way to the centre of the room and look up, they will not easily see the other exit in the very centre on the ceiling. Spotting this will be difficult, requiring either a passive Perception of 17 or success on a DC 17 Wisdom (Perception) check, or sending in a scout (like a familiar) to examine the room. This exit is roughly 8 ft. in diameter, and is the source of the dripping from above. This leads to an irregular and wet tunnel leading upwards 30 ft., opening into another 50 ft. diameter spherical chamber above, save for the pool and there is not exit in the ceiling. Traversing the passage means a half climb rate unless otherwise abled, and is also slippery. Success on a DC 15 Strength (Athletics) check is required for attempts to climb.

This upper chamber is partially covered in webs from the middle of the walls spanning upward. Hanging from the centre is what looks like a uvula made from webbing. Within this uvula is a glass ball filled with acid.

The main feature of this room will be the resident. Agnesstrix, a drider (Monster Manual, page 120), has squeezed her large body into the vertical tunnel and is five feet from the bottom opening. Her body is relatively soft, and easily compresses to allow for moving through this passage. Because she possesses the Spider Climb feature, traversing this passage is not an issue for her. She is hungry and not a little mad, and could behave in wildly unpredictable ways.

Her favourite ploy is to retreat mostly up the way of the passage, hanging her drow upper torso down the tunnel and crying for help. When the unsuspecting heroes, or even other lesser predators, come up the passage to save or attack her, she will unleash her wand of web (Dungeon Master’s Guide, page 212) down the passage and trap prey in the passage. She will then shoot her longbow at restrained foes.

If that fails to ward her chamber from intruders, she will then cut the strand suspending the glass orb in a globule of webbing, dropping it down the tunnel. Those in the tunnel will need to succeed on a DC 15 Dexterity saving throw to avoid the globe. Should anyone fail, every player character 5 ft. upwards from that failing character, and everyone below them to a range of 10 ft. will be sprayed with acid. Marching order is imperative here, as is the distance between PCs. Make sure to determine this as they enter the tunnel, if they enter the tunnel.

If the globe strikes anyone, a direct hit will do 4d10 acid damage, with the splash doing 2d10 acid damage to characters in the splash range. Those who suffer splash damage will take half damage with success on a DC 15 Dexterity saving throw.

Characters who emerge from the top of the hole will be subject to another wand of web attack. If foes dodge this attack, she will scramble up the walls so she can attack the intruders at range with her longbow. Knowing PCs, the answer is yes, the webbing on the walls is flammable. Those in a web spell (from the wand of web or otherwise – as per Players Handbook, pages 287, 288)  will suffer 2d4 fire damage should they be in contact with the webs.

Agnesstrix is no fool. If things look like they are not going to work out for her, she has no problem using the last charge of the wand of web to cover her retreat back down the tunnel, as her Spider Climb allows her to pass through these with ease. Should she be defeated, or even if she escapes, there will be dessiccated foes below the webbing stuck to the wall in tiny crevasses in the cavern. Anyone who takes 10 minutes to dig through these bodies will find scattered bags of coins and gems, as well as an elaborate silver-framed hand mirror with a shattered mirror in it (see below).

Agnesstrix – Drider (as per Monster Manual, page 120)

Wand of web, several small bags of coins and gems, totaling 500 sp, 250 gp, two small sapphires worth 200 gp each, a bag of small ruby shards worth 50 gp, a string of pearls worth 100 gp, and a small and elaborate silver framed hand mirror with a spider motif that has a shattered mirror surface worth 50 gp.

Being trapped in the passage by webs, burned by acid and then sniped with a longbow seems like a bad day. If your player characters are having horrible luck, keep in mind that Agnesstrix is a Drow at heart, and may still torment and taunt her foes. She may even just try to Grapple with the lead restrained victim so that she can stick them to the wall for a later feast. Should a TPK happen, this might be the fate, as they possibly awake stuck to the ceiling of the upper chamber.

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