ToME: the Tales of Maj'Eyal

being eternal, i take it there is no way to drop them?

It's false advertising on their part. They're just a bit persistent is all.

hrm, welp i finally got one to 0HP even though my berserker obviously counts on lots of physical damage, which was reduced to 0.
LONG fight.
But i got him down to 0, and he would then get another 150 or so HP. Did this twice. Shall I assume 3rd time is the charm?

EDIT: Fight I'm referencing took place in the backdoor to the armory in the far east. Unless that particular Eternal Bone Giant is supposed to be indestructable, with 100% physical damage resistance, I think i encountered a bug.
I went to another pride, found another eternal, and dropped it pretty easily. Definitely not the same experience.

Hrm, only encountered one with an Archmage, and he only resurrected once. Maybe he has a cooldown on the resurrect and you must kill him quickly? Also note that any enemy must reach -1 HP to die.

yeah i'm probably killed about 10 or so at this point. that one was definitely different, maybe buggy

Sounds like it's not the cause here, but the generation in T4 does throw up noticeable differences between individual bad dudes - which seems like a good thing, can find e.g. that one uruk or whatever is majorly fire-resistant while his buddy's perfickly toastable. There's so much behind-the-scenes stuff like that which adds touches - the archer might be about to whack you with slime-coated arrows, depends what he picked up at the barracks this morning - is very good.