Board Thread:Questions and Answers/@comment-149.135.147.108-20130425043302/@comment-4632427-20130425050553

I can't give an exhaustive list off the top of my head, but I'm pretty sure it's limited to rocks, defensive structures, and the Ancient Sentinel's arms. All of those except rocks will still take damage from the initial hit, they just won't get the Poison DoT status applied to them. Of the above-listed items, the Sentinel fragments are the only ones that are units you can bring on offensive missions, and they're currently almost impossible to acquire.

The Dragon and the Salamander also have excellent Fire resistance on their armor, making poison attacks about them do very little damage as long as their armor lasts.