Ye Blue Bookes of danjerus andde koruptynge knowlidge, the finalle tombe of Five Great Wizzards.
A very ornate and very old looking spell book. Chock full of spells, most of which are unreadable by any magic user. The ones that can be read, unfortunately, don’t have the affect the mage is looking for.
On a location with numerous webs, and at least one big spider, there is a something inside a cocoon. It is humanoid in shape, still moving. If the heroes free it (not before they kill or drive away the spiders), they meet a ... zombie!
The poor zombie wandered the dungeon alone, and tried to kill a big living creature (= a spider). The spider used the usual treatment, even if this victim did not look tasty. The zombie can be easily killed as any other zombie. It got but several doses of spider-poison, so can be something worth if it is extracted. You can mention to a druid or ranger the fact the spider had no poison anymore.