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."
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.