From the announcement:
You didn’t really think we were going to set a game in a city damned by the Lord of Undeath without some new Death models did you?
These Sepulchral Guard are the former warriors of the city of Shadespire. Unlike many of the mindless shambling automata of the Mortal Realms’ undead legions, these once-proud warriors retain shards of their memories from before the cursing of their city, and each is a unique individual in their own right.
In the game of Warhammer Underworlds, this warband plays in a unique way. They’ll have numbers on their side against most opponents, but they lack the furious damage output of the Bloodbound, or the resilience of the Stormcast Eternals. Instead, this Deathrattle force favours a player with a considered, strategic approach to battle. They have plenty of tricks up their ragged sleeves to tip a combat in their favour, chief amongst them being the Sepulchral Warden’s ability to inspire and bolster the other undead warriors around him.