Here is how I beat and captured all of them to use in my army.
Got 100 zombies (any fodder will do) as well as my companions, though the companions were fairly useless.
Sent the zombies in.
When they were swarmed, I charmed the pounder immortal. While the zombies were being killed 1 at a time, the pounder knocked out his friends easily as they have decent reach.
Then facing the pounder in the second battle I sent everyone in, they all failed miserably except I had some cavalry spare, THANKFULLY I had artimenner with a balanced jousting lance. I had kept my cav back just in case. All my companions were going down, only a few had blunt weapons worth much anyway, the cav all did have a spare blunt weapon though as I use them to capture fleeing enemies sometimes.
I started retreating everyone but the cav back, while they went in and charged down a hill from behind, artimenner nailed it in one hit with the balance jousting lance
. I did a bit of fire damage to it before hand, maybe 70 pts worth and had people shooting at it for a
short while with the dwarven rifles. I don't think they have loads of health, just decent armor, so don't overdo it.
I love these kinds of advanced challenges, and I don't mind in this case that it makes me overpowered, as they are very late game things to do, I hope to see more of them! What comes AFTER the immortals
, something with AoE damage perhaps so I can't bum rush it with zombies, that'd be a nice challenge.
-edit
therex55213 I don't know the conditions under which they spawn as they just did while i was playing, but if you want to be spoiled as to what the troop looks like as well I can do that, click for full sized version.
Like the balrog, if you get this troop is should cost you at least 1k to keep, maybe even 2k for these guys but that might be overkill I suppose
but darn he seems to be 'good' for the purposes of demons/undead doh!