Now think of this as a reversed charge attack. I have played Empires: Dawn of the Modern World before, and one such unit, the Korean Koryo Hwarang, has this ability: to kill enemy units when half of its HP is reached.
I remembered watching the movie Last of the Mohicans back in middle school. The ferocity of the Natives portrayed in the movie gave me an inspiration: the Iroquois Warrior (unit only available in editor) with aforementioned ability added and slight modifications will be a theoretical unique unit for a future civ called Algonquians.
Here goes:
Iroquois Warrior (cost: 60 food, 50 gold). Algonquian unique unit that will slay an enemy unit when half of it’s HP is reduced.
Stats:
HP: 80
Attack: 7
Armor (MA/PA): 1/1