How the Devil ...?

[Cainehill]

Just got done losing a battle in which the enemey forces had routed long ago, and the only enemy (Vanheim) unit left was an ice devil, which somehow ... healing during the battle.

I went through the battle replay several times; the only spell the devil cast was Quickness; its magic items consisted of Winged Shoes and an Amulet of Antimagic, with the default(?) Hell Sword. Looking at the hell sword, there's no mention of life stealing.

So - any idea how the devil the devil was going from 8 HPs in one turn, to 30 the next, to 54? Near as I can tell, I had the battle one, save for this inexplicable healing, given the devil didn't seem to have regeneration, life stealing, or any other units that might have been healing him. Only thing I can think of is that the Hell Sword does have lifestealing abilities that aren't mentioned?