Oh wow. I was going through the Anvil Runes for the Dwarfs, and I noticed something. Dwarfs have three standard Anvil Runes in 8th Edition's base army book, and a further three Ancestor Runes in the Storm of Magic Supplement, which are buffed up and more powerful, and I've come across something very interesting that I found relevant.
The standard Anvil Runes are:
Rune of Hearth and Home: Targets every single Dwarf in 24" (and only Dwarfs). Grants Immune to Psychology for a turn.
Rune of Oath and Steel: Targets a single Dwarf unit, giving +1 to their armor saves for a turn.
Rune of Wrath and Ruin: Cracks the ground open to vent magma at enemies, dealing 2d6 Strength 4 hits to a unit distributed as shooting.
Fairly tame stuff, but I think you can cast all these runes as bound spells once per turn each, so it makes sense that it's limited. Now, here's the big stuff. The Ancestor Runes:
Ancestor Rune of Grungni: Targets a number of friendly units equal to the number of successful strikings (notice that this isn't restricted to Dwarfs like the regular Anvil Runes). All allies affected by this have the Fight in Extra Ranks special rule and reroll all failed to hit rolls for both shooting and close combat for a turn.
Ancestor Rune of Grimnir: Same as Rune of Wrath and Ruin except it has a wider area of effect.
Ancestor Rune of Valaya: Targets a number of friendly units equal to the number of successful strikings, not Dwarf restricted. Heals targeted units in the exact same way as Regrowth and grants all affected units Unbreakable for a full turn.
Why is all this relevant? Well, we've seen Anvil Runes in the quest before, but here's why I think it's important:
Codrin's archers were to be next to disengage, but you suspect them of jumping the gun as the greenskin tide surges forth again as they are freed of the arrows that had been tormenting them. But Kragg has no need to withdraw, and to your surprise his magic does not manifest to torment the greenskins but to bolster the men, and a roared battlecry is shared amongst the mercenaries as the Dwarvish enmity of greenskins floods through their mind and strengthens their arms. An instant of silence falls upon the battlefield as those Orcs closest to the men are struck down and none are willing to step forward to take their place, and the bloodlust of greenskins furthest from the enemy clashes with the cowardice of those closest, and for a second the combined shouts of thousands of greenskins commingles into an eerily familiar roar of frustration.
What Kragg did here was not Oath and Steel or Hearth and Home. Aside from the fact that those Anvil Runes only affect Dwarven units, the effect presented here does not fit what they do. He used the Ancestor Rune of Grungni on them, which grants fight in extra rank and reroll hits, represented as "Dwarfish enmity of greenskins" strengthening their arms and flooding through their minds. That might also explain this:
"And finally, and to my shame, most unexpectedly - the bravery of the line of men. All manner of Umgi answered my call to arms, but I never guessed them capable of receiving the charge of a maddened Waaagh with such fortitude. Their showing today would do credit to a line of Ironbreakers." You prevent an eyebrow from raising, knowing that the line of men had more than a little assistance in their actions, and instead of watching Codrin receive the praise for his men you're watching to catch the surly look Kragg shoots at King Belegar. Interesting.
Kragg didn't just use a regular Anvil Rune, he got so caught up he used an Ancestor Rune, a greatly treasured and powerful artifact of the Golden Age to empower the Undumgi. I can understand Belegar wanting to cover that up to prevent outrage from the wider Dwarf community.
This has been pointed out a long time ago, but it's also the reason why Mathilde noted the Undumgi had such an affinity for Dwarfs and picked up Khazalid nearly as fast as she did. Their souls were literally transmuted with the spirit of Grungni.