"Necropolis" - changes to creatures of levels 6-7.

OR
My version
Unit------dark knight--------death knight-----------champion of darkness----
ability-------------------------curse strike----------zombie strike-----
ability-------------------------fear attack------dispel spell

Unit----------Death-----------Harbinger of Death-------------Banshee------
ability-------aura of terror----------aura of terror----------------aura of terror---
ability--------------------------devastating grip--------screeching wail--
ability------------------------------unholy word or strike of sorrow-----

Added after 2 minutes
in general, in the original, they only differed in the wail and grip, as I suggested

Added after 1 minute
This aura is present in the ordinary grade of nightmares; it lowers the morale of nearby units.