Garuna in Heroes 5

Each killed enemy troop (summoned troops considered, too) increase the Attack of all the creatures in his army by +1 for each 6 levels of the hero.

At certain times in Orcish history there have been warriors particularly attuned to the Blood Rage inherited from their Demonic ancestors. Garuna, born of a Shaman who was participating in a ritual sacrifice in spite of her advanced pregnancy, was brought into the world in the midst of a ceremony of bloodletting and intense fervor. Unsurprisingly she has become one of those famous "Blood Drinkers", and whenever a group of enemy units is wiped out she and her own troops become even more formidable on offense.