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.)
On some of the islands off the coast, the rites of the local fertility god revolve around ceremonial death and rebirth. The religion's priests have overcome this cycle, however: Each of them is actually undead, ceremonially slain and "reborn"! Their religion is otherwise unremarkable, being an odd offshoot of the mainland's religions. The priests vow to resist their undead cravings, seeing these as the "cycle of life" attempting to reclaim their spirits.