I want to say that in the campaign for Arantir, I upgraded the special ability, i.e., "Scream of Terror," and in combination with powerful items (Staff of the Damned, Cloak of Deadly Shadow, Ring of Sinners, and whatever else), after the scream, the enemy almost always ended up with negative morale, by about 5-6 points.
Added 2 minutes later
What level was it, and which hero did you play as?