Stabbey is correct, the elemental arrows are virtually OHKO for any character. This isn't a "oh I could have prepared for that", it's "oh shit I'm dead" because poison arrows deal too much damage in to little a timeframe.
It's easier at higher levels, since Jahan's spells scale appropriately and Rangers get debuff removers, but at low levels it's like seeing the kobold pull out a vorpal longsword with a permanent true strike on it.
