How has your encounters with dark elves and dwarves been in your campaigns? Do you see these races as twisted parodies of their lighter cousins? Do they strike fear and helplessness in your players? Have their houses risen to infamy in your world setting?
The Underdark/Darklands has spawned many strange creatures in its hidden depths. However, the Drow and Duergar were more warped by the presence that spawned by it. Twisted through catastrophic events that lead to their retreat to this dark underworld. Demons, dark gods and goddesses and alien races influenced them and helped to warp them from creatures of good and light to sadistic slavers and fleshwarpers.
The progenitors of driders, dark magic and twisted demonic contracts, the drow and duergar houses rose to pinnacle murderous rulers of the underdark and darklands of many world settings. How do you portray drow and duergar in your campaigns? My current GM Tips video discusses using them in your campaign setting.