Delrith and Angerbeard previewed Game Master Mode and went on an adventure led by Larian Dev turned GM Eduoard. You can watch the video here:
https://www.youtube.com/watch?v=nlfUrUOYgYk
Game Master Mode will be available on release September 14th. Read more about it here: https://www.kickstarter.com/projects/larianstudios/divinity-original-sin-2/posts/1880437