Witch Slayer is a steel sword in The Witcher 3: Wild Hunt that comes in 2 different forms:
Witch Slayer (crafted)[]
Crafting Requirements 
Min. Required Level: Journeyman blacksmith
Witch Slayer (basic)[]
It can be found, along with a flawless ruby, in the Isolated Hut where Dandelion is being held. It can also be found as random loot or purchased from the following merchants:
- All blacksmiths in Skellige
- Merchant at the Isolated Hut on Hindarsfjall