This is pretty much how all the prior Matt Mercer one-shots have been. From Doom Eternal, to Warcraft, to Diablo III, they are usually one shot 5E homebrews that Matt Mercer makes. To be quite honest, I wish they would sell each one shot on the Crit Role website as I also wanted to see how he has made/set up everything. So far the ONLY one I've seen that you can actually purchase is the Doom Eternal one.
Part of me thought that somehow, Mercer was given playtested rules of the Dark Souls TTRPG to help mold/formulate the mechanics of this one shot. Although, the Stamina seems to be something "similar" to its Position mechanic. Except you can't defend or reduce damage if you're out of Stamina, which is spent to do things.
You can tell the homebrew Stamina system has some major wrinkles, but it did a great job making me feel kinda like a Souls game. I know what it feels like to run out of stamina and get clobbered by a boss!