Based on the second campaign of Critical Role (the first being The Legend of Vox Machina) in which a group of voice actors play dungeons and dragons.
In The Fleching and Moondrop Travelling Carnival of Curiosities, Jester and Fjord visit a hall of magical mirrors, one of which reflects them as humans (rather than tiefling and half-orc). Their reflections are those of their voice actors, wife and husband Laura Bailey and Travis Willingham.
In Dungeons & Dragons spells require verbal, somatic, and/or material components. The material components are often ignored by players who can substitute them with a casting focus like a staff or an instrument (as seen in The Legend of Vox Machina with Allura and Scanlan respectively). To illustrate Caleb's poverty and flavour the magic, Liam O'Brien chose to forego the focus on Critical Role and lean into the material component usage, which is reflected in how magic is portrayed in The Mighty Nein.
Set roughly twenty years after The Legend of Vox Machina in the world of Exandria. While Vox Machina dealt primarily with the continent of Tal'dorei, Mighty Nein centres on the Wildmount setting, home of Lord and Lady Briarwood (from The Legend of Vox Machina Season 1) prior to their takeover of Whitestone.
D&D copyright races cannot be named but can be depicted. As such, Jester and Mollymauk aren't referred to as tieflings, Essek isn't referred to as a drow, and Yasha isn't referred to as an aasimar.