Plagues and other great diseases are important parts of history and some settings. They defy man and may even defy God in their swift and terrible punishment upon the body of society.
My issue with modifying/removing dwarves and elves is that the PC’s may want to play them.
One of the most powerful tools found in the World Building 102b article is the Worksheet. Here is a place to put the settings you might make with them.
Serpens Necto is a mask made of snake skins stitched together and crudely painted in white. With this on a person can bind people to their will under the right conditions. In darkness the effect of the mask is greatly enchanced by illumination from under by a candle.