Attacks made with the Slayer Sword have the Flaming Attacks and Killing Blow special rules. If Skulltaker is fighting in a challenge, attacks made with the Slayer Sword also gain the Heroic Killing Blow special rule.
Source: Warhammer Armies Project: Unofficial 9th Edition
Attacks made with the Slayer Sword have the Flaming Attacks and Killing Blow special rules. If Skulltaker is fighting in a challenge, attacks made with the Slayer Sword also gain the Heroic Killing Blow special rule.