In the War-Com article when they announced The Hunt, they mentioned that the Gods and Heroes rules were still in effect and had been incorporated into the FAQs. If you check the FAQs, you will find them there. Kragos' new warscroll is the errata for Orruk Warclans. Archaon's warscroll is in the Errata for StD. Nagash's new warscroll is in the errata for Soulblight. The changes to the core rules are on the last page of the errata and not in their respective sections, which would be easier to deal with.
It is the Sons of Behemat ability on the Mega-gargants warscroll card. Son of Behemat: If a spell or ability would slay this model without any wounds or mortal wounds being inflicted by the spell or ability, this model suffers D6 mortal wounds instead.
This ability is also on all of the mercenary warscroll cards for the megas as well (from the new app). The mancrusher gargants do not get this ability.
