Different races inhabit Discworld and move from place to place depending on the age of your campaign.
Bigfoot type of immortal humanoid, enjoy having their heads cut off.
Always evil, always up to no good.
Most widely spread race on Discworld, you can't walk a mile overground without tripping on them.
Yeth, Mathter?
Refugees from Faerie.
Any member of fauna that can speak another species' lingo whereas his brethren can not.