[Shadekeep]

I was thinking that Naturalists might not just have insight into harvesting antivenoms, but also know some natural palliatives for certain kinds of poisons. Like antivenoms these would be highly specific to the poison's source, but in game terms could be generalised as a difficult roll (4/IQ or even 5/IQ) for the Naturalist.

As for Physickers, I think they should be able to slow or halt multi-turn poisons, if such things occur in your campaign settings. The TFT system is more geared towards immediate combat effects, but one can imagine a slow-acting poison that does a small amount of damage every turn for a number of turns. Physickers should be able to counter this effect to some degree.