Hugonauts

How does Gotrek's Avatar of Grimnir special rule interact with the Shattering Blow special rule of Hammerers (and other such abilities, which allow attacks to inflict mortal wounds in addition to normal damage)? Would each roll of 6 to wound inflict both a wound and a mortal wound, because each 6 is considered to be both an attack and a separate instance of the Shattering Blow ability? Will Shattering Blow inflict at most a single mortal wound, because it is one ability? Or, will Shattering Blow cause the wound to deal both a wound and a mortal wound, but be subsequently reduced to only 1 point of damage between them, because it is a single attack? Imagine a unit of Hammerers attacks Gotrek, rolling 10 successful wound rolls; five of these wound rolls are 3s, and five of them are 6s. Which (if any) of the following would be correct? - Gotrek suffers 10 wounds, and 5 mortal wounds. - Gotrek suffers 10 wounds, and 1 mortal wound. - Gotrek suffers 5 wounds and 5 mortal wounds.