Skaven often use the highly unstable properties of warpstone to create devilishly deadly weapons.
Source: Warhammer: The Old World Online Rules Index
Warpstone WeaponsURL Copied!
URL Copied!
A hand weapon carried by a model with this special rule has the Magical Attacks special rule and an Armour Piercing characteristic of -1.
Note that this special rule only applies to a single, ordinary hand weapon. If the model is using two hand weapons or any other sort of weapon, this special rule ceases to apply.