One of the faces of modern Dungeons & Dragons, Matthew Mercer is no stranger to letting mass audiences into the worlds he’s created.

Mercer has been the Dungeon Master for “Critical Role,” a weekly livestreamed D&D game featuring a group of eight professional voice actors and friends, Mercer included, for five years. The show has been viewed tens of millions of times on YouTube and Twitch.

D&D is more popular than ever, and it’s easier than ever to get a group together to play — even while practicing social distancing amid this coronavirus pandemic.

The latest D&D sourcebook — a guide for players at home to create their own tabletop adventures — is a collaboration with Critical Role called “Explorer’s Guide to Wildemount.” A preview of the book is being offered for free online while people are mostly stuck at home as part of a nationwide effort to slow the spread of the virus.

"It's like a childhood dream that I never really dreamed because I didn't think it was possible," Mercer told USA TODAY.

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The roughly 300-page book has about 150,000 words written by Mercer over two years, he said. It includes a brand-new system of magic called Dunamancy, which takes its cues from quantum physics and astrophysics, Mercer said.

While home games might be hard to come by with states across the nation issuing stay-at-home orders,playing D&D with immediate family members is always possible. There are even options for people self-quarantining alone at home.

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Roll20 is a widely used, browser-based “virtual tabletop” utilized by more than 5 million people, according to its website. Through Roll20, it’s possible to buy D&D sourcebooks and play games with friends with video conferencing. An adventure preview from “Explorer’s Guide to Wildemount” is available for free on the website.

“Social distancing doesn’t have to be isolating,” Roll20 wrote in a blog post on its website. “We know you’re at home and we hope you find yourselves in good health and good company. If you’re missing your friends and family during this difficult time, we want to help.”

Fans of the book and of “Critical Role” have reached out with positive messages regarding the book, Mercer said.

“It’s been their immediate solace in the anxious-ridden times we’re currently entering,” he said. “I’m glad it could be there for people. I wish this wasn’t the case at all, but it’s the silver lining.”

Being a fan of “Critical Role” isn’t a prerequisite to appreciating Mercer’s sourcebook. The campaign setting of Wildemount is the also setting for the second season of the show, which began in 2015. It’s a darker setting compared to the first world Mercer created, called Tal’Dorei. That first world was the “classic” fantasy setting compared to the “morally gray” Wildemount.

“I wanted it to be kind of a deeper and more… diverse and ambiguous take on what a fantasy world can be,” said Mercer, who is known for his voice work in popular video games like "Overwatch" and "Resident Evil 6."

“For this, everything is relative, and the choice is really up to you, who you decide is on the right or wrong side of history.”

The book has lore tidbits and additional mysteries for fans of the show, Mercer said. It also works as a good starting point for those who are new to the world of D&D and provides new, potentially inspiring, material for seasoned D&D veterans, he added.

“To really think about all different facets of each element of the world and how they affect each other and how that world building can not only be interesting and evocative, but presented in a way anybody should be able to step up to the table, take it and be excited about what they find,” Mercer said.