First off They will no longer be called the Drow called them Dark elf
Second Dark elf are made from all other Excluding half elf
Abraxas Demon Lord of Forbidden Lore and Magic Created a ritual that Corrupts elfs and Turning down into demon worshippers of whatever demon lord turned them.
And last all dark elf Do not live underground anymore. They live in the abyss Serving the demon loads that turn them.