One thing becomes apparent as you read through Waterdeep: Dungeon of the Mad Mage. It's a big dungeon. The overwhelming majority of the content consists of the dungeon levels themselves - maps and keys - 23 levels in all. There are a few pages up front about dungeon history and attributes of the dungeon, and a small appendix with several new monsters and magic stuff. Everything else is dungeon content.
There's not a lot of space devoted to storyline, plot hooks, and how to run an engaging campaign in Undermountain - the referee is mostly on their own. Hopefully that's a skill you picked up from earlier editions, or from your friendly neighborhood OSR blogger. Probably the most useful thing readers can glean from my game reports is how I've woven exploration of the dungeon into the themes of the campaign. I've been effective at presenting storylines that encourage the players to explore deeper. I'll focus special attention in the game reports on our use of plot hooks and rumors to integrate Undermountain into campaign play so you get ideas for your own games.
The idea behind the first campaign arc was focused on finding the headquarters for the Xanathar's Guild. Several important Waterdeep citizens had been replaced by Intellect Devourers, including a high ranking member of Force Grey. Several of the player characters were working their way through the ranks of Force Grey and were personally involved in uncovering the intellect devourer plot. The Black Staff, the arch-wizard that commands Force Grey, invited them to a special briefing at Black Staff Tower.
"We need to find a furtive way into Xanathar's Guild headquarters. It's located beneath the underground pirate city of Skullport. There are entrances to Skullport from within the sprawling dungeon called Undermountain located beneath the Yawning Portal Tavern. I'd like you to scout the first several levels of Undermountain to find the best way to Skullport; from there, spend enough time in Skullport to discover how Xanathar's agents come and go. Once you have that well-mapped, return for further instructions."
All of the players were already interested in exploring Undermountain, although only two of them were aspiring members of Force Grey. But everyone thought scouting several levels of Undermountain, making their way to Skullport, and locating the entrance to the crime boss lair, was fairly interesting and the whole party got behind the mission. I think many of the typical Forgotten Realms factions could provide alternative motivation to get started with Undermountain; I liked the urgency the "invasion of the body snatching intellect devourers" created.
The first dungeon level is rather generic, with the ubiquitous "dungeon bandit hideout", some typical scavengers like trolls and carrion crawlers, and several hideouts for humanoids working for Xanathar's guild. Many of the bugbears on this level are host to intellect devourers, which greatly reinforced our theme about the grave threat posed by Xanathar's alliance with the Mind Flayer(s). Whenever combat would start with a group of humanoids, I'd ensure the correct bugbears would maneuver towards the characters with low Intelligences. The bugbears would eventually be dropped to zero hit points, and the Intellect Devourer would materialize next to the dead host body, ready to brain zap another big dumb galook and jump into a new cranium. Several player deaths were delivered this way! Great fun for the DM, and a way to spike the tension at the table. Intellect Devourers are terrifying.
The other bit I greatly enjoyed on the first level was the "revenant". There's a dead cleric named Garke trapped in a well where his murderous companions dropped his corpse before looting his stuff; Garke has returned as a revenant to exact vengeance, just as soon as someone helps him out of the hole. He has an unerring sense of location to hunt his betrayers. Garke became an interesting ally for the players, because they could take advantage of his help for as long as they pushed forwards after his tormentors (which drove the players down to level 2 quicker than they may have liked). It's balanced by the fact the revenant is a powerful ally, a nigh unstoppable force of destruction.
The party at this time consisted of Ace, an elven blade dancer wizard; Bosko, a goliath barbarian; Alfred, a rapier-wielding duelist (fighter); Teukros, a Drow assassin/rogue; and Virsk, a northman cleric. Spoiler alert: most of them died on level 3, but we'll get to that story eventually. At this point in their career, they motored through level 1 with minimal casualties and accompanied Garke around areas of level 2 for a bit, at least until he had pounded enough of his murderous ex-companions (the Fine Fellows of Daggerford) into a bloody pulp that his spirit was able to travel onwards to his rest.
I've mentioned in a previous post that Undermountain is "balanced" for 4 players starting at 5th level. For a larger group, I'm just counting up total levels. So the first level is meant for 20 levels of characters (4 5th level characters); the second level is 24 levels (4 6th level characters) and so on. There are various "arch gates" on each dungeon level that are tied to character level as well which I'm adjusting due to our larger group size. In this way I've got a sense how well they'll handle the challenges.
Level 2 was fairly fun. There's a goblin market and a problem with the goblin boss who wears a special magic item called a "circlet of human perfection" that changes his shape into an attractive (naked) human. Goblins don't have the same modesty as people so the players got a little tired of seeing the goblin junk flapping around in front of them when Yek danced and gamboled around.
There was an area where most of the players fell into deep covered pit trap, without any light sources, and couldn't figure out how to get the pit open from the inside. Meanwhile, Virsk, the cleric, was left outside one of the pits, and had to battle alone against an undead beholder zombie while the schmucks tried to free themselves from the pit traps. Virsk still brags about single-handedly killing a beholder (and everyone chimes in "it was already dead…").
This campaign originally started with Waterdeep: Dragon Heist, and some of the potential outcomes of that adventure include the players owning their own Waterdeep tavern (Trollskull Manor) and winning a 50,000gp royal treasure. Our players ended with both outcomes. With the money, they tried to find a powerful magic item on auction (random magic item) and they were able to bid on and buy a Daern's Instant Fortress. One of their first priorities when they explore a new level of Undermountain is to find a safe redoubt with a ceiling high enough to allow the instant fortress to deploy. We've had entire games where they defended the fortress against a siege of dungeon monsters.
There was also a challenging treasure on level 2 that tied into their tavern ownership. Much of level 2 is an old dwarven mine dating back in Undermountain history to the Melairkyn dwarves - dwarven mines, dwarven temples, breweries, and so on. One of the distant chambers has a large trove of magically preserved Melairkyn ale in large barrels. The upper levels of Undermountain are extremely light on treasure, and the Melairkyn ale is several thousand gold pieces (140 or so barrels at 40gp each, but each barrel is 400 pounds of weight). One of the players was a Zhent agent and was able to secure a small mercenary force to secure the straightest path from the ale storage to the Yawning Portal. They negotiated a cut with Durnan (the proprietor of the Yawning Portal) and then brought a healthy supply back to Trollskull Manor. The players have maintained a side business as tavern owners, they run a Zhent black market out of the basement, and engage in some light politics in the city.
Level 3 of Undermountain is really good, and where this dungeon exploration campaign really took off. We'll start our look at level 3 next time!