“ Pick up a pathology/microbiology book, and add the diseases/syndroms to your game. Your players will freak out.
Coughed at? Diphteria. or tuberculosis?
Drunk from a muddy stream? Or just walked through? Well, let us introduce you to schistosomiasis...
Hit by a stream of energy? Too moch mana is ust like too much radioactivity - perhaps all mages could develop cancer early if too powerful...”
“ Actually a real-world fungus, just heard about it. A fungus that tastes well and all, no ill effects. UNLESS you consume some beverage, even 3 (three) days after eating it. Then you become really sick, pains, vomiting, all the fancy stuff. Was really used to cure alcoholism. May be a joke or to make sure the heroes spend their time focused on the mission.”
“ The PCs are hired by undead to rid their village community of an invasive necromancer.
As the PCs make their way, wherever they are going, they spot two zombies. The zombies approach but before the cleric can turn them, one starts throwing coins at the PCs while the other pleads with them, unable to pronounce the letters 'L' and 'H' due to some missing gums. 'Peeth issen...no 'arm...coin...peeth issen!'
If the PCs don't slaughter the two zombies immediately, they will eventually come to learn that the two were chosen to find help by their brethren. The zombies want to hire the PCs to rid their community of an unwanted pest. An opportunistic necromancer.
Apparently, a small benign community of undead have taken residence in an abandoned village, living out their undeath as peacefully as the undead can. Recently, a malicious necromancer has invaded the village, and plans to enslave the entire populace with his malignant spells, raising a small army.
The PCs must battle the vile necromancer, even as he animates the very folks who hired the PCs in the first place, to slaughter them.”