The Death Guard are Nurgle's main troops in their fight against all things clean. They're getting a new codex for 40k next year and we get the first look at some of their changes that'll be coming within with this preview.
From the article:
The Death Guard codex is on its way early next year, and it features five key changes to their rules which will have an enormous impact on how these putrid servants of Nurgle operate on the battlefield. Over the course of the week, we’ll be looking at each of these new rules in greater detail and discussing why Mortarion’s Traitor Legion is set to become more disgusting in battle than ever before!