From Sewer Crawl to Showdown: Behind the Curtain of Session 10 – Facing Grum’shar

A DM’s Look at Planning and Running a Climax in Waterdeep: Dragon Heist

Every D&D session is a mix of structure and chaos—and sometimes the best moments are the ones you didn’t plan. In Session 10 of our Dragon Heist campaign, the party confronted Grum’shar, a minor Xanathar lieutenant with a memorable face and a less-than-memorable exit. What was meant to be a straightforward dungeon crawl turned into one of our most cinematic sessions yet.

Here’s a breakdown of what went into planning it, what actually happened at the table, and what I learned along the way.

The Plan: A Straight Shot Through the Xanathar Hideout

Going into this session, I had three primary goals:

1. Deliver a climactic encounter with Grum’shar that felt like a payoff from earlier sessions.
2. Showcase the Xanathar hideout as a real, functioning lair—claustrophobic, confusing, and crawling with danger.
3. Bring the “Friend in Need” arc to a satisfying close with the rescue of Floon.

I prepped a simplified map, assigned rough behaviors to patrolling enemies, and figured out possible branching routes to Grum’shar’s chamber. The party had already cleared the goblin guards last session, so I expected them to sweep the rest of the lair tactically—room by room, until they triggered the final encounter.

Of course, that’s not exactly what happened.

The Twist I Didn’t See Coming: “I’m a Goblin… Carrying a Mattress.”

There’s a moment every DM dreams of: the table goes quiet, a player leans forward, and says something completely insane—and you realize it just might work.

That moment belonged to Maple, our druid, who disguised himself as a goblin carrying a mattress to infiltrate the next room. It was absurd, hilarious, and oddly plausible. I could have shut it down—but instead, I ran with it. The absurdity helped lower the group’s guard right before the duergar fight, creating contrast and making the tension pop when combat started.

Lesson learned: embrace the weird. Some of the best immersion comes when the world feels flexible enough to accommodate your players’ chaos.

Combat Execution: Grum’shar’s Last Stand

Grum’shar isn’t a powerhouse on paper. He’s a CR 1 spellcaster with a few nasty tricks and a memorable look (thanks, eyeball tattoos). I needed to boost his presence without breaking the encounter’s balance.

Here’s how I did it:

• Gave him better positioning: He used the layout to ambush with allies and control the battlefield.
• Added a duergar backup just before to foreshadow a serious threat.
• Let Grum’shar monologue and taunt a bit—just enough to make him feel personal.

The fight was short, sharp, and punchy. The players had to work together, and every class brought something important to the table. No single character dominated, and everyone walked away feeling like they contributed to the victory.

Player Highlights: Spotlight and Satisfaction

One thing I was proud of this session was how balanced the spotlight felt. Everyone had a moment:

• Doc tanked like a beast and brought the fury.
• Kiril led investigations and disarmed threats with stealth.
• Maple… disguised himself as a goblin with a mattress.
• Raven landed killing blows with arcane menace.
• Clover kept spirits high and allies empowered.

As a DM, it’s not about who shines the most—it’s about whether everyone got to shine at all. That happened here, and it’s something I’ll be chasing again.

What Worked (and What I’d Do Again):

• Pacing the dungeon like a funnel: Optional side rooms, with one route clearly escalating toward the boss, helped players stay on track without feeling railroaded.
• Saying yes to nonsense: That goblin disguise is now legend in our group.
• Letting Grum’shar die dramatically: Even weak villains can feel iconic if you give them a spotlight death.

What I’d Refine Next Time:

• Add more environmental description to exploration scenes. Players are hungry for sensory cues.
• Flesh out interrogation opportunities more. NPCs caught alive should have clearer motives and personalities to create richer scenes.

The Payoff: A Rescued Friend, A Dead Villain, and a Party That Felt Like Heroes

By the end of the night, the players had rescued Floon, defeated Grum’shar, and taken a disgusting skin-flap trophy that made everyone laugh and gag in equal measure. They left the lair stronger, tighter as a group, and with the sense that this was the end of Act I.

For DMs: trust your prep, but be ready to throw it out. For players: don’t be afraid to bring your weirdest ideas to the table—you just might steal the show.

Session 10 was a great reminder that you can’t plan magic—but you can create the space where it happens.

Your Turn!

Have you ever had a session go completely off-script in the best way? Did your players derail your dungeon with disguise kits and dumb luck?
Share your own session war stories, DM tips, or glorious party moments in the comments below—or tag me on your favorite platform. Let’s swap tales from the table and keep the inspiration rolling!