Sepulchure/Gravelyn's Shadowscythe Undead Army is a lot similar to dage's(or you could say Dage's is a lot similar to them) but since Dage is or was an apprentice of Nulgath he has the knowledge and power of both the undead and those of the void, pushing him further above the two in terms of power(and might explain why he has so many followers). The Shadowscythe are focused on pure malignant evil, much more evil than Dage and Nulgath. Dage is evil but not evil enough. Nulgath is a being of un-comprehensible power but as he is a being of the void, he holds an ambition for world/universal conquest. The ShadowScythe is just pure wickedness. Even if they're not that powerful, they don't want to die not trying... if they do die.