Critical Role’s Matthew Mercer just revealed 1 foundational rule that all Dungeon Masters should use

The beauty of running tabletop role-playing games as a Dungeon Master is that you’re practically guaranteed to run your games differently from everyone else. Professional DMs — like Matthew Mercer, Aabria Iyengar, and Brennan Lee Mulligan — are no exception to this, which is why their styles and narrative approach can be so interesting to watch for aspiring DMs.

Mercer’s style of DMing has inspired other players for years, so much so that the Mercer Effect — where new players expect their TTRPG games to run exactly like Critical Role’s setup — remains a hot topic in RPG communities. That said, I’m certainly not immune to picking up tips and tricks from Mercer, and there is one vital rule in particular that, regardless of your style, all DMs should add to their arsenal.

The latest episode of Critical Role’s current miniseries, Age of Umbra: Sallowlands, has Mercer leading his cast of Elden Ring-esque vagabonds across a blistering desert region, where they’re quickly caught up in a dust storm. As the players ruminate on what to do next, Sister (Laura Bailey) suggests finding shelter. The downside: she would have to roll with a disadvantage. While fellow players scrambled to help, Bailey wondered aloud if she could use her experience Dust to Dust, which, based on its name, sounded like it would help in navigating the storm. In Daggerheart (Critical Role’s answer to a D&D-style tabletop game system), experiences allow players to spend Hope to add a +2 modifier to their roll.

However, there was a catch. Bailey wasn’t certain her experience would be useful. Instead of shutting Bailey down, Mercer employed the “yes and?” rule, best known for its use in improvisational theater, to ask how she would like to use the experience to help her and her fellow players. While Bailey didn’t end up using the experience, Mercer’s not simply shutting Bailey down reminded me of the importance of “yes and?” as a tool for Dungeon Masters. Collaboration is the heart of tabletop role-playing games, and the worst thing a player or DM can do is try to shut down that flow between one another.

It’s not the first time that Mercer has used this rule in either the Sallowlands miniseries or throughout his time as Dungeon Master in Critical Role’s campaigns. Mercer did so in the premiere episode of Sallowlands by allowing Jennifer English to create one of her character Dillwyn’s experiences on the spot, allowing her to fashion a reason why her character would be able to see through the fog and spot enemies. This allowed English to make a vital move in combat while also keeping the narrative flowing without complication.

It’s important to note that Mercer’s use of “yes and?” doesn’t mean he or other DMs who use the rule are pushovers who let players get away with everything. On the contrary, the use of dice and other rules within tabletop games means success isn’t always guaranteed. For example, if English hadn’t rolled well, her experience wouldn’t have helped her or the rest of the players navigate their enemies in the dust storm, regardless of whether Mercer allowed her to make that decision.

However, what is guaranteed is the rule encouraging creativity within players. Even if the result doesn’t end up working out, DMs stepping back to let their players attempt something — no matter how ludicrous it sounds — refines the narrative of the story you’re all telling, which, for groups where story is one of the most important tenets, is exactly what you want.

Image: Critical Role

Speaking from my own experience as a former militant rules lawyer, the “yes and” rule was the foundational rule that helped me improve as a DM. Instead of shutting people down immediately and making them feel as though they couldn’t contribute to the scene or combat, I met my players on their level and lost my fear of playing it wrong in the process.

Regardless of what sort of Dungeon Master you are, the “yes and” rule is exceptionally useful in inspiring confidence in players while also setting limits when necessary and feels like an essential tool for any DM to have in their back pocket. Ultimately, it’s a core element of improvisation, which — at least in the case of Critical Role and Mercer — helps make their performances so endearing.