Nurgle has a melee-centric roster which is arguably the most resilient in the game, able to outlast practically any enemy attack. Divided between mortal and daemonic units, Nurgle's roster has access to a large selection of incredibly sturdy melee infantry and monsters with large health pools, plus faster and more mobile war beasts, monsters and cavalry, as well as a tiny number of powerful ranged options. They also have access to two powerful lores of magic full of both damaging and healing spells.
The downside is that most of Nurgle's units are very slow, and thus are especially susceptible to missiles, magic and flaming attacks. Their core units are also fairly bad at inflicting damage, with low stats in Melee Attack and Weapon Strength, meaning that much like a disease they must wear an enemy down slowly over time.