The warrior's footfalls echoed on the cobbles. His breath steamed in the cold, frosty air. He heard the frantic movement of assailants in the shadowed alley shuffling to surround him.
The warrior laughed. It was a bitter, dry laugh. "It won't do you any good. I feel no pain. Prepare to meet Balor."
You find a patch of edible funghi. They taste well and all, no ill effects. UNLESS you consume some beverage, even 3 (three) days after eating it. Then you become really sick with pains, vomiting, all the fancy stuff. As a gift or good meal, it could be a cruel joke or to make sure the heroes spend their time focused on the mission. And the fine soup you had in the inn yesterday could have some in.
(Inspired through a real-world fungus. Was really used to cure alcoholism.)