Poisoned Weapons and Etherealness ???

[Wuppin]

The fatigue damage of Sleep Vines is armor-negating, I'm pretty sure.

You might be right, but from the in-game description (at least for the mandragoras) the are not armor negating or AP. I think that there are other units with similar attacks such as tenticles on some units you get from crossbreeding but to the best of my knowlege it is not the case with manikins and mandragoras. Perhaps the in-game attack description is wrong? Can anyone answer this more definitively?

And, for the record, I agree that with a 25% chance to hit the non-magic-but-still-poisoned attacks of tritons are the cause for your dead ethereal unit.