Necrophage Oil

The Witcher

"Necrophages are accustomed to poisonous vapours. Yet even the most rancid ghouls and graveirs cannot withstand the poison wounds inflicted by a blade coated with Necrophage oil."

A blade coated with Necrophage oil inflicts increased damage on necrophages. Damage inflicted on necrophages is increased by 100%.

Source

The Book of the Swallow

Notes

One user has reported that Necrophage oil is ineffective against drowners and drowned dead and though they might appear to be necrophages, they are not in fact included in that class, so this would make sense.

The Witcher 2: Assassins of Kings

Geralt begins the game with four of these. The formula can be bought from Anezka in Lobinden.

Journal entry

This blade grease increases sword damage dealt to necrophages - i.e., all creatures that devour corpses. It is the most effective oil against monsters of this type.

This oil is ineffective against humans and monsters other than necrophages.

The Witcher 3: Wild Hunt

Necrophage oil returns as an oil in The Witcher 3: Wild Hunt.

There isn't a formula for this as Geralt already has the knowledge to create this at the beginning of the Prologue.