If a model with Killing Blow rolls a 6 to wound in close combat, they automatically slay their opponent – regardless of the number of wounds on the victim's profile. Armour saves and regeneration saves cannot be taken against a Killing Blow. Ward saves may be taken as normal.
Killing Blow is only effective against Infantry, Cavalry and War beasts. Against other troop types, a successful Killing Blow only inflicts one Wound which Ignores Armour saves and Regeneration.
Note that if a Killing Blow attack wounds automatically, then Killing Blow does not come into play. Unless otherwise specified, Killing Blow applies only to close combat attacks.
For the purposes of combat resolution, successful Killing Blows score the same amount of Wounds as the slain model had remaining until the point of the Killing Blow was inflicted.
Unless specified, Killing Blow only applies to the model's normal Close Combat attacks.