The Host of 'Dimension 20' Reveals the 1 Thing Dungeon Masters Need to Know

There's a reason Brennan Lee Mulligan is one of the best DMs around.

I’m sitting in the back section of seats at the Bell House, but in about 30 minutes, this hip Brooklyn venue for concerts and podcast recordings will transform into a fantasy world where six hapless adventurers return to high school to fight a monster in front of a packed house. It’s all thanks to Brennan Lee Mulligan, one of the most animated and descriptive Dungeon Masters among a rising class of DMs who broadcast Dungeons & Dragons campaigns to thousands of fans — in this case, Mulligan’s CollegeHumor show, Dimension 20, is available on the company’s streaming service Dropout.

There’s no shortage of Dungeons & Dragons content on the internet, from Critical Role to Relics and Rarities, but Dimension 20 might be the funniest of them due to Mulligan’s comedic storytelling.

“Brennan’s a lifer, and he would be doing this whether it was for his job or not,” Ally Beardsley, who plays cleric Kristen Applebees in Dimension 20, tells Inverse that night. “For a wrap gift on the first season, he gave each of us a D20 die that he has had since he was 10.”

dimension 20 fantasy high
Promotional image for the live recording at The Bell House, featuring Mulligan top-right and the characters of Fantasy High on the bottom-right.

Dimension 20 Season 3, a modern urban fantasy called “The Unsleeping City,” kicked off on July 9, but I’m at the Bell House on June 24 to watch an official side quest that expands on Season 1’s “Fantasy High,” a John Hughes-inspired adventure set in a fantasy high school with ‘80s vibes.

With over two decades worth of DM experience, what advice does Mulligan have for his fellow Dungeon Masters? Here’s his one biggest tip for new DMs, along with his memories of getting started with D&D’s 2nd Edition, and so much more.

This interview has been edited for brevity and clarity.


brennan lee mulligan
Brennan Lee Mulligan recording Season 1 of 'Dimension 20'.

What piece of advice would you give any aspiring Dungeon Masters out there?

If given a choice between keeping the rule books happy or your players happy, remember that the books will never pat you on the back and tell you that you did a good job or look at you and say, “This is the most fun night I’ve ever had in my life!”

Rules are important, but they’re in service of you and your friends being able to tell an awesome exciting story with sudden twists and danger and risk. Ultimately, you are more responsible to the experience being had at the table.

How do you feel like your early days playing D&D has influenced your career as a performer?

I started as a D&D player in 2nd edition in 1998, at a point where D&D had very much dipped in the public consciousness, from the heyday of the ‘70s and ‘80s. All props to my mom who thought it would be really good for me, and it was in terms of personal joy it has brought to my life. My most important and best friendships have thrived and grown in connection to this game.

I had the player’s handbook that had the jacked Conan the Barbarian guy with the helmet and a sickly green bearded wizard on it bashing down a door. 

D&D 2nd edition handbook
Cover art for the 2nd edition Advanced D&D player's handbook.

It feels very full circle in a way because I started D&D and larping and stuff like this when I was 10 years old, and then found my way through that to performance, comedy, and improv. I did that for a bunch of years in my 20s and still do, but then started working at CollegeHumor.

There was a part of me that thought as I’m doing comedy, when people ask me how I got my start, I’ll tell them Dungeons & Dragons. Yet here I am with the two things feeding into one another.

What were your early experiences like as a DM?

The first experience I had as a DM was all of my friends at the dining room table when I was 10 years old. We were all 10-year-old children. You can imagine: No one listened. It was pure chaos. I wrote my own adventure. And Corey, it was bad. It was very bad.

Everyone made little 10-year-old boy edgelord badass characters like a wolf-man. I wrote an evil sorcerer character who was invincible unless you learned about and cared about his tragic backstory, and all these heroes were like, “I don’t give a fuck about this guy’s tragic backstory! I’m being played by a 10-year-old boy!” And I was like, “Well, you’re all dead.” I was a little monster myself.

Everyone went home. I turned to my mom — and even as a 10 year old — said, “This was the most stressful day of my life.” Then I scheduled another session for the very next weekend.

dimension 20 bloodkeep
Dimension 20 Season 2, "Escape From the Bloodkeep," is an all-evil campaign in a world that feels like a 'Lord of the Rings' epilogue.

Being a Dungeon Master is stressful!

Very! But it’s a beautiful thing. There’s something about the game that’s like falling off a bicycle on your first time riding. You think, “Wow, that sucked — but we’re not stopping here. We’re going to get back up and try again until we’re good at this.”

I’m so grateful that I did because even to this date, my preferred pastime activity is still playing D&D, despite playing so much for work.

When you play for fun, do you get to play as a character at all or is it mostly DM-ing?

Were that I had the option to be a player. No one invites me to play their game!

I feel that. Since I started DM-ing, now it seems like that’s all I’m able to do.

You’re never going to play again. Truly.

Brian Murphy, the DM for Not Another D&D Podcast, was kind enough to have me play on a guest in his campaign recently. It was the most fun I’ve had in ages.

That’s not because I don’t have fun as a DM. I love being a DM. But it’s good to not let yourself get totally lopsided. It informs your DM-ing to remember what it’s like to be a player. I think that’s important.

Would you ever want to make Dimension 20 or another campaign you’ve run into a bonafide canon source book?

If I could turn my long-running homebrew campaign into a source book for D&D — which even saying it out loud, I feel bashful and shy. If that could ever happen, I would rocket off the face of the planet in a beam of pure light and joy and feel a feeling of accomplishment that I would never be able to top again in my life.


New Dimension 20: The Unsleeping City episodes are released every Tuesday only on CollegeHumor’s Dropout.

Media via CollegeHumor (1, 2, 3, 4), Wizards of the Coast