Halaster Blackcloak: Full Guide to The Mad Mage Beneath Waterdeep

Far beneath the city streets of Waterdeep, beneath the lair of the Xanathar Guild and the Yawning Portal tavern, on the lowest level of a sprawling megadungeon waits Halaster Blackcloak — the architect of Undermountain, the Mad Mage himself. 

In this guide, we’re going to break down what we know about Halaster Blackcloak, what he wants, and some of the ways you can roleplay him as a dungeon master. 

Halaster Blackcloak, The Mad Mage 

Medium Humanoid (Human), Chaotic Evil

  • AC: 14 (17 with mage armor)
  • Hit Points: 246 (29d8 + 116)
  • Speed: 30 ft.
  • STR 10 (+0) DEX 18 (+4) CON 18 (+4) INT 24 (+7) WIS 18 (+4) CHA 18 (+4)
  • Saving Throws: Int +14, Wis +11
  • Skills: Arcana +21, History +21, Perception +11
  • Damage Resistances: Fire, lightning (granted by the blast scepter, see “Special Equipment” below)
  • Senses: Darkvision 120 ft., Passive Perception 21
  • Languages: Abyssal, Celestial, Common, Draconic, Dwarvish, Elvish, Infernal, Undercommon
  • Challenge: 23 (50,000 XP)
  • Proficiency Bonus: +7

Special Equipment

Halaster wears a Robe of Eyes (which affords him a 360 degree range of vision, 120 feet of darkvision, advantage on sight-based Wisdom (Perception) checks, and the ability to see invisible creatures and objects, as well as into the Ethereal Plane, out to a range of 120 feet) and wields a Blast Scepter (a very rare magic item that requires attunement and can be used as an arcane focus.

The Scepter allows its wielder to cast thunderwave as a 4th-level spell, save DC 16 without expending a spell sloth, and also grants them resistance to fire and lightning damage. 

Halaster also wears a horned ring that allows an attuned wearer to ignore the magical restrictions of Undermountain — which largely involves preventing people from leaving it or accurately using scrying magic within its walls.

Arcane Recovery: (1/Day). When he finishes a short rest, Halaster recovers all his spell slots of 5th level and lower.

Legendary Resistance: (3/Day). If Halaster fails a saving throw, he can choose to succeed instead.

Rejuvenation: If Halaster dies in Undermountain, he revives after 1d10 days with all his hit points and any missing body parts restored. His new body appears in a random safe location in Undermountain.

Spellcasting: Halaster is a 20th-level spellcaster. His spellcasting ability is Intelligence (spell save DC 22, +14 to hit with spell attacks). He can cast disguise self and invisibility at will. He can cast fly and lightning bolt once each without expending a spell slot but can’t do so again until he finishes a short or long rest.

Halaster has the following wizard spells prepared:

  • Cantrips (at will): Dancing lights, fire bolt, light, mage hand, prestidigitation
  • 1st level (4 slots): Mage armor, magic missile, shield, silent image
  • 2nd level (3 slots): Arcane lock, cloud of daggers, darkvision, knock
  • 3rd level (3 slots): Counterspell, dispel magic, fireball
  • 4th level (3 slots): Confusion, hallucinatory terrain, polymorph
  • 5th level (3 slots): Bigby’s hand, geas, wall of force
  • 6th level (2 slots): Chain lightning, globe of invulnerability, programmed illusion
  • 7th level (2 slots): Finger of death, symbol, teleport
  • 8th level (1 slot): Maze, mind blank
  • 9th level (1 slot): Meteor swarm, wish

Actions

Blast Scepter

Halaster uses his blast scepter to cast thunderwave as a 4th-level spell. Each creature in a 15-foot cube originating from him must make a DC 16 Constitution saving throw.

On a failed save, a creature takes 5d8 thunder damage and is pushed 10 feet away. On a successful save, the creature takes half as much damage and isn’t pushed.

Legendary Actions

Halaster can take three legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature’s turn. Halaster regains spent legendary actions at the start of its turn.

  • Cast Spell: Halaster casts a spell of 3rd level or lower.
  • Spell Ward (Costs 2 Actions): Halaster expends a spell slot of 4th level or lower and gains 5 temporary hit points per level of the slot.

Lair Actions

On initiative count 20 (losing initiative ties), Halaster takes a lair action to cause one of the following effects:

  • Halaster targets a volume of unoccupied space or solid stone no larger than four 10-foot cubes within 30 feet of him, turning the open space to solid, worked stone or vice versa.
  • Halaster causes one door or archway within 30 feet of him to disappear and be replaced by a blank wall, or he restores a door or an archway previously removed in this way.
  • Halaster deactivates or reactivates one of Undermountain’s magic gates. The gate must be within 120 feet of him.

Source: WDMM, page 310

Who Is Halaster Blackcloak?

Halaster Blackcloak has been a recurring character throughout the history of Dungeons & Dragons since the early 1990s

He’s cropped up in various Forgotten Realms novels, like Escape from Undermountain, Elminster in Hell, and Realms of the Underdark as well as a whole slew of adventures — first in The Ruins of Undermountain in D&D 2e and later in Expedition to Undermountain and Waterdeep: City of Splendors where several of his own patented spells, including Halaster’s Blacksphere and Halaster’s Grasping Hand were introduced to the game.

These spells are sadly absent from 5e.  

In D&D 5e, Halaster Blackcloak was made the focal antagonist in the 2018 module Waterdeep: Dungeon of the Mad Mage, which updates both Halaster and the sprawling, deadly megadungeon of Undermountain for the latest edition of the game. 

Halaster Blackcloak is almost certainly one of the most prodigious magic users in the entirety of the Forgotten Realms. 

He is a 20th-level spellcaster and unparalleled when it comes to creating and controlling a vast network of portals and gates throughout the world and the planes beyond.

Halaster regularly uses his teleportation expertise to capture and imprison powerful entities from throughout the multiverse in Undermountain — stocking his dungeon to the rafters with all manner of strange and dangerous creatures. 

Exactly why he does this is both simple and frustratingly unsatisfying: he’s as mad as a box of froghemoths. 

Halaster
© Wizards of the Coast

Why Is the Mage “Mad”? 

Halaster Blackcloak wasn’t born mad, and it wasn’t until he came to Undermountain that he began his transformation.

The answer to why Halaster — not to mention a number of his apprentices, several of the powerful creatures that live in his dungeon and even Durnan (owner of the Yawning Portal tavern) — are touched by madness lies thousands of years in the past, long before even the aged Halaster was born. 

Millennia ago, the mountain of Waterdeep was home to Aelinthaldaar, the capital city of the ancient elven kingdom of Illefarn.

For reasons unknown, the elves decided to vacate their city, and, as they left, they cast a powerful spell that erased all traces of Aelinthaldaar from the world. 

While the spell worked, it also created a permanent “knot” in the Weave — the fabric that underpins all magic. 

This knot lies deep underground and isn’t something that can be seen, felt, or undone, but it can cause madness to bloom in the minds of mortal beings who dwell near it for too long.

  • Waterdeep: Dungeon of the Mad Mage (2018)

The influence of the knot in the Weave permeates all of Undermountain, and the madness it cultivates usually manifests as an “obsession” with the dungeon as well as a desire to remain in or near it. 

For all his power, Halaster remains unaware of the knot and has been compelled over the centuries to explore, expand, and transform Undermountain into an extension of his own “mad” desire for yet more power and control. 

Halaster: Architect of Undermountain

More than any other villain (maybe with the exception of Strahd and Castle Ravenloft), Halaster Blackcloak is intrinsically linked with his lair: the megadungeon of Undermountain. 

Halaster came to the base of Mount Waterdeep over a thousand years ago in the company of seven apprentices.

Together (along with the aid of hundreds of strange and powerful beings summoned from across the multiverse) they raised a mighty wizard tower and set about doing whatever it is high-level wizards do — wearing cool hats and messing with the fabric of reality, most probably. 

However, over the years, Halaster was seen less and less by his apprentices.

The archmage tunneled further and further beneath his tower, first breaking into the Underhalls — a complex of tunnels and rooms built by the dwarves around a mithral mine beneath Mount Waterdeep.

The dwarves were all dead, and in their place, a war between clans of duergar and drow waged in the dark. 

Halaster gleefully began a crusade against both the drow and the duergar, driving away the dark dwarves once the mithral mine ran dry.

He also rounded up the remaining dark elves, trapping some of their souls for use in his dark magic while twisting the bodies and enslaving the minds of others. 

Then, already feeling the warping effects of the knot in the weave, he dug ever deeper into the space under the mountain. 

Using his underground complex as a base of operations, Halaster traveled to other planes and distant lands, collecting strange and dangerous creatures to live as prisoners, servants, or guardians in Undermountain.

Populating and defending the dungeon became an obsession. Over time, the mage’s preoccupation with Undermountain electrified his eccentricities and infused him with an air of unconcealable madness.”

DM’s Corner: How To Play Halaster Blackcloak 

In Dungeon of the Mad Mage, Halaster is described as giggling and muttering incessantly with a demeanor that can change on a whim.

In short, he’s supposed to be played as more or less completely divorced from rationality, but we’re also told that “contrary to appearances, however, Halaster is alert and attentive to the activities and preparations of all beings near him.” 

I think it’s important to interrogate Halaster’s “insanity” and what it means for dungeon masters who want to portray the Mad Mage. 

Sometimes, roleplaying games (and the fantasy genre as a whole, I suppose) struggle with representations of “insanity.” 

Specific diagnoses of mental disorders are slapped insensitively onto characters as a form of “edgy” roleplaying advice, which is gross; or a character is simply written off as “mad” or “insane,” which somehow manages to be both gross and quaintly old fashioned. 

Either way, none of it actually helps us run a compelling character at the table.

Madness, it would seem, is license for writers to give up on making their character make sense — even when made less problematic by the addition of backstory like “an undetectable knot in the fabric of magic is making them mad.”

Issues of representation aside, it doesn’t give us a lot of ammunition if we want to make Halaster into a compelling (or at the very least interesting) villain. 

What Does Halaster Blackcloak Want? 

When you run Dungeon of the Mad Mage, the module suggests you choose (or randomly determine) one of the six possible motivations for Halaster, which range from tricking the player characters into taking out one or more powerful monsters or factions in Undermountain to just scaring the adventurers so badly that they turn around and leave, telling other people to maybe leave the wizard’s dungeons alone. 

Honestly, other than the rather convoluted plan involving returning a disgraced (also “mad” because everything in this module has to be mad) Waterdavian noble family to power, installing them as his puppet government in the city above, all of Halaster’s plans share the same two traits: 

  1. They have basically no effect on the world outside of Undermountain, a place the PCs have essentially no stakes in beyond a big dungeon full of treasure. 
  2. The plan is basically unknowable to the PCs but also isn’t a mystery to be unraveled; rather, it’s just something that happens in the background. 

None of this is very satisfying, and I think Halaster’s madness is the thing that lets the module feel like it can get away with such piss-poor motivation for a villain. 

We can do better. 

Figuring out how to run the Mad Mage is, I think, a matter of focusing on the obsession angle of the knot in the weave’s influence. Thinking of it as a thing that just “makes mortals mad” isn’t helpful. 

Thinking of the knot in the weave as an amplifier, a lens through which the light of ambition becomes a death-ray and logic is warped and fragmented like a kaleidoscope, well, that’s something we can work with. 

Halaster — like most other wizards — desires power, knowledge, and control over the world around him. He came to Undermountain seeking this power and he found it.

The mountain has amplified these tendencies exponentially, and the whole dungeon complex is essentially a monument to his power over other life forms as a result. 

This is, I think, a lot more actionable as a DM than “he’s mad, lol idk.” It’s also something you can use to shape the characterizations of other NPCs throughout the adventure as well.

Find out what pushes their buttons, and then crank those elements of their personality up to 11. 

Let players know about this when they meet intelligent undead who seem to be the only rational people in the dungeon.

Fill empty corridors with clashing murals, ambitious sculptures, and abandoned pages from half-written novels and spellbooks. The dungeon is an amplifier for ambition, desire, and drive. This is how it makes you mad. 

Once the players realize this, play on that dramatic irony by having Halaster recruit them as research assistants, sending them out to gather data on “the strange behavior of everything in this dungeon.”

Obviously, if the players point out that this is also affecting Halaster, it’s Finger of Death time. 

Playing Undermountain 

The final thought I have on portraying Halaster involves playing Undermountain as an extension of the Mad Mage.

This entire place was created (or at least heavily modified) by Halaster, stocked with creatures he kidnapped from throughout the multiverse, and is essentially one big physical manifestation of his obsession — his mad grasping for power, knowledge, and control. 

In addition to using NPCs and monsters (areas of Undermountain are also populated with slightly bizarre statues of Halaster, which is something I like to dial up even further) to big up his mythos, Halaster’s lair actions and regional effects are a great way to continually reinforce the idea that this is his domain. 

You can read Halaster’s lair actions above (I would have these take effect regardless of whether or not the mage is actually present) and see his regional effects here: 

Regional Effects

When Halaster is in Undermountain, the following effects can occur in any location within the dungeon or in any extraplanar extension of the dungeon:

  • A magical scrying sensor appears, taking the form of a ghostly, 1-foot-diameter humanoid eye surrounded by motes of light. The sensor is stationary, though Halaster can reorient the eye to face in any direction. Halaster can see through the eye as though he was in its space. The eye can’t be harmed or dispelled, but it winks out within an antimagic field. A scrying eye lasts until Halaster ends the effect (no action required).
  • A minor illusory effect is triggered, as though Halaster had cast minor illusion in an area. Common illusions include the echo of rattling chains, the distant sound of explosive spells being cast, a dusty cloak or a rusty helm floating as though worn by an invisible figure, and illusory footprints appearing on a dusty floor.
  • Silent apparitions of dead adventurers drift through halls and rooms as though they are lost. An apparition can’t be harmed, and it doesn’t acknowledge creatures or objects in any way. It can’t be dispelled but is suppressed within an antimagic field.

Very few villains give you, as the DM, so much license to mess with the party. I would suggest using it, but remember that everything you do should be for the benefit of Halaster’s desire for power, knowledge, or control. 

Use minor illusions to create ethical tests or puzzles for the PCs. Then, as the illusion fades away, leave the players staring at a small glowing eye that gives the distinct impression that it’s taking notes.