For several years, legendary Dungeon Master and voice actor Matthew Mercer has been hosting live Dungeons & Dragons campaigns via YouTube and Twitch in a series called Critical Role . At the beginning of the series, he started out with modest battle maps drawn out on paper. Over time, Mercer's maps became more complex. He made hand-painted elements, three-dimensional map pieces, and used immersive music and lighting. And of course, Mercer's voice acting helped with the overall character buildin…