In one of those games that are already pretty much won and good for experimenting, I was quite entertained to find out that the unfettered eater of the dead was quite susceptible to enslave mind!
This, of course, left me with a very evil grin 8)
I proceeded to take the eater, along with a few astral mages with spell focuses and 'enslave mind' orders out to a contested but highly populated province and pillage the daylights out of it.
10 or so turns later, I unleashed the 2000hp, 200hp/turn regenerating behemoth of destruction on my unsuspecting enemy. 500 machakan infantry after that, the eater was suffering from having lost both eyes, but taking it stoically as it rolled all over the opposition ;p
Thinking about it, hellbind heart is probably a better approach, as that way I can keep the unfettered as a commander ( eeep heroic health ) and equip it with the chalice/ring of regeneration for pure regenerating insanity 8)