Crones are a Creature/Monster in The Witcher 3: Wild Hunt.
"Sister crones, hand in hand, terrors of the sea and land, thus do go about, about: thrice to thine and thrice to mine, and thrice again, to make up nine. -Macveth, Act 1, Scene 3
The isolated corners of our world harbor creaturs older than humans, older than academies and mages, older even than elves and dwarves. The Crones of Crookbag Bog are such creatures. No one knows their true names, nor what breed of monstrosity they in fact are.
Common folk have given thee three sisters the names Weavess, Brewess and Whispess, and call the whole threesome "The Ladies of the Wood", or simply "The Good Ladies." The Crones act as the true sovereigns of Velen, whose inhabitants they help survive through harsh times in return for unquestioning obedience. They wield powerful magic, but one different from that of mages. They draw power from water and earth and are bound to the land in which they live. The Crones can hear everything that happens in their woods, predict the future, twist the threads of human lives and bring blessings as well as curses.
The Crones seem for all intents and purposes to be immortal. Magic elixirs keep them from aging and allow them to take the appearance of young women. These elixirs and their mystical ties to the swamps in which they live also give them supernatural strength and vitality."
- Notes on Lore and players notes go here.