The Sea hides many secrets in its depths, here are 30.
The grudging gift of thankful mermen, a fine blade with a bit of baggage.
Deep within the heart of the Great Woses, lies an inland sea that few care to visit. Nevermind the ogre-infested swamps that surround it, the place is just disgusting. While known by many names – the Belching Sea, the Eternal Loogie, Gluumraag's Blessing and sometimes, the Slimy Deep – most simply call it the Sea of Snot.
This is a wretched tome of oceanic blasphemy; a foul water-stained, bone-white binder of bitter dead-men’s secrets and a guide to Nautical Necromancy useful in the hands of the young sea-faring necromancer or the Great Lich Umeen herself.
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.)