This could be a mechanical Clan Skryre attachment or an evolved mutation, the results are the same - another appendage wielding a weapon.
Source: Warhammer Fantasy: 7th Edition
Tail WeaponURL Copied!
URL Copied!
A model with this additional blade, spike or mace can make an additional S3 Attack at the user's WS and Initiative. It can be used in addition to other attacks including an additional hand weapon or even a magic weapon, although it gains no magical properties.