“ 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.”
“ A weapon of war created by an extinct race, this rat appears normal but is a simulacrum - beneath it's mangy fur is a body of bronze. Commanded by words in a lost language, wherever it goes a virulent and lethal plague follows. The cure is similarly obscure.”
“ During a public holiday in the small town of Wyrmbersch, the Mayor is accidentally killed by a statue which falls from the roof of the Town Hall. As shocked spectators crowd around the body, they discover that the Mayor, at the moment of death, shape-shifted into a squat, stunted humanoid figure, it's grey skin dominated by bony ridges and lumps. How long was the Mayor an imposter? And who else in the town isn't what they seem to be?”