Here's what goes on behind the scenes in the nerdworld business' coolest alliance

• Brennan Lee Mulligan and Matthew Mercer have formed a strong alliance in the nerdworld business.
• "D20" and Critical Role have sold out major venues like Madison Square Garden and the Wembley Arena.
• But both men are also close friends, and they worked together on "Downfall," CR's latest campaign arc.

Brennan Lee Mulligan of "Dimension 20" fame remembers when he first met Critical Role's Matthew Mercer, and relates that anecdote with the infectious joy of a man who's found his gaming soulmate.

Mulligan was working on "Um, Actually," a web series on the streaming platform Dropout, and for one episode, he was tasked with writing errors into a round of "Dungeons & Dragons" combat laid out in comic panels. Mercer was a guest on that November 2018 episode. At the time, "Critical Role" — the "D&D" Twitch stream that turned the company Mercer co-founded into a key player in the nerdworld business — was just taking off.

Mercer, as a "rules lawyer," had to spot all the mistakes in Mulligan's slate. He not only got all of them, he found ones the other man hadn't even listed.

When filming wrapped, they stood at the elevators at that West Hollywood studio, talking about their "D&D" games.

"There's love at first sight, and this is one of those variations," Mercer told BI. "Like, this is a person I immediately know: 'I'm going to know for a very long time, and I look forward to seeing them again.'"

These two men have now formed a formidable alliance in the nerdworld business. The shows they front get fans to pack arenas: "Dimension 20" sold out Madison Square Garden for their January 2025 gig, and "Critical Role" has filled venues from Wembley Arena in London to the Greek in Los Angeles.

Beyond that, they also have leadership roles behind the scenes. Mercer is the chief creative officer at Critical Role, working with his eight friends on everything from Amazon-backed animation series' to board game ventures. Meanwhile, Mulligan is one of the major creative minds at Dropout, a streaming platform that's now gunning for Emmy nominations.

Mulligan helmed his first Critical Role miniseries, EXU Calamity, in May 2022. Mercer then returned the favor, and game mastered for "Dimension 20's" Ravening War," a six-episode campaign that aired in May 2023.

On to 'Downfall'

Mulligan told BI he had long watched Critical Role, and that he got to dive deep into Mercer's lore while working on EXU Calamity. Then he was invited back for "Downfall" — a three-episode arc that aired in July.

Mercer told BI that working with a guest game master like Mulligan on Critical Role requires a "strong sense of trust" because of how dear the stories in Exandria are to him.

"I was anxious at the possibility of trying to live up to what I saw in my head, then had the joyful realization that somebody else that I trust can do it better justice than I think I ever could," Mercer said of Mulligan.

Mulligan said he would go to Mercer with "broad strokes" of where he planned to take the narrative. But Mulligan had "total freedom" to improvise while role-playing at the table, which he found "really gratifying."

"With Matt, it's never restrictive. It's much more like: 'Here's an area that I need to protect for something coming in the next campaign, and then everything else here is the playground," Mulligan said.

Crafting Aeor

Mulligan said it helps that he and Mercer are always on the same page — from their familiarity with mythological references to similar visions for the story's direction.

Together, they built the sprawling landscape of Aeor, from a glamorous speakeasy where robots and humans can party together to the brutalist architecture of key city wards. They also created a battle set together, setting the stage for where the gods of the Exandrian pantheon warred against dragons, monsters, and powerful mages.

"We pulled minis together for that battle and really pulled out all the stops," Mulligan said.

"I was right off camera behind the curtains watching the whole thing as it was happening, just giddy and crying, and it was wonderful," Mercer said.

Mercer and Mulligan agreed that storytelling and work aside, they're just glad they get to hang out with each other.

"As a person who grew up challenged to find community at various points in my life, and the passions and things that I loved were not the easiest to find people to share it with," Mercer said.

Mercer says telling stories for his friends is his love language, and he's glad to be able to do that with Mulligan.

"The CR crew have become the closest people in my life that aren't blood," Mercer said. "What's great about these collaborations is it allows that family to expand, it allows more people to come in and be that community," he added.

Now, Mercer's back in the game master's seat for Critical Role's campaign three. I asked if he would want to be a player at Mulligan's table for a change, perhaps piloting a fan-favorite character, the elven wizard Essek Thelyss.

"Nothing wrong with pitching it. I'd love to," Mercer said, adding that if the opportunity comes up for another adventure with Mulligan, he's game.