“ In one region of a forest, all of the trees are identical, down to the leaves and the twigs. If the PCs carve something into one of the trees, it could mystically propigate until it covered all of the trees, or could vanish since it was not carved into the one true tree.”
“ 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.”