Poisoned Weapons and Etherealness ???

[Vynd]

With Tritons you will be facing 27 attacks per turn - even with etherealness you are going to be hit a lot and it only takes a couple of lucky rolls in this case to wipe you out.

Yeah, I think Sheap has the answer here. Etherealness is good for stopping attacks from hitting, but it doesn't do anything to reduce the damage from those that do hit. That's what you need Mistform for. But against a bunch of Tritons you'll never get a chance to cast it.