1 - The poison clouds from pit vipers cannot hit you with their physical part if you are standing still. However, they WILL hit you EVEN if you are standing still if your merc moves in the same spot (or very close) due to teleporting.
2 - Witches cannot curse you if you have a shrine or another curse already active. They WILL attempt to curse your merc (and very likely hit you as well) if he is "clean", but ONLY if he is closer to them than you are. Else, their AI will tell them to either shoot blood stars at you (happens most the time) or move towards you (if far) or move away (if close). No cursing if their closest target has a shrine or is already cursed.
3 - Several poison clouds are more dangerous than single ones, for some reason. They get stronger if there is fanaticism or might around.
4 - Nihlathaks hit recovery seems strange. Could be my min damage is JUST too low to force hit recovery.