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.
Appearing a small ballista bolt, this ‘bolt’ is actually an arrow used by a god from a long-dead pantheon. Some sages theorize it was a weapon crafted by Loki to slay the world tree. Why it was never used escapes them however.
The spear has a divine-level anti-plant effect. When driven into the soil point first, a ever widening circle of destruction radiates out from the point, killing any plant material. Perfect for holding a kingdom’s food supply for ransom.
How far it extends depends of course on the GM, of course.