Spoiler Alert! for those who are yet to take part in The Heart of the Vortex, this is your last spoiler warning!

***********************************************************************************************************************

Ok, with that out of the way, here goes. I am looking for some clarification on the wording of The Cost for a Black Crusade ambition on Page 136:

"Compare the Infamy threshold set at the beginning of the campaign to the player's current level. In the coming challenge, the group will have to face a number of Grey Knights equal to this figure, though they should not be forewarned of this fact."

So, what does that mean, exactly? If the threshold is 140, and the player has an Infamy of, say, 100, does that mean they face 40 Grey Knights?

What that means is this:

I started with 30 Infamy at the beginning of this campaign. I now have, oh, 90, because i'm awesome like that.

90-30=60

They will face down 60 grey knights.

Note: as you've undoubtedly read, the whole point is to be absurdly hard to the point of being a joke. And throw the GKs at them in teams of 10 or something, if you have players like mine, they'll be killing 3 GKs per round.

It'd make a lot more sense to just make it one grey knight called Kaldor Draigo, tbh.

The situation is supposed to be overwhelmingly difficult in order to express the impossibility and inevitability of death and to eventually feel the embrace of Nurgle. Death and the end comes to us all and standing against dozens of grey knights/daemons/xenos/assassins is a clear message to the players of that. If you had one massive encounter then players might think they can beat it as it is still just one figure at the end of it all which can be outwit, outmanoeuvered and kept dancing around whereas hundreds of enemies, the players will soon realise that there really is going to be no way out.

But the challenge is to also not shy away from those odds either, to show that one is willing to give their lives in the service of Chaos willingly. So yes your interpretation and numbers are correct. In terms of deploying them you may want to either use small hoards worth or if you're feeling brave, stupid and can somehow speed up the process to some unparalleled degree then map out all of them. I did actually see someone who did that once on something else, quite amusing to watch him:

"Ok so that's 12 damage to guardsman 8."

"16 damage to guardsman 32..."

Course the look on a players face when you unveil the magnitude 30 hoard of khorne aligned deamon princes is just too funny.

Oh one little house rule I added when making this adventure was the inability to use or burn infamy points. mechanically this kept the players from just burning all their infamy since they will need all of it latter anyway, also the idea of a deamon prince with only 3D10 infamy sounds weird. Fluff wise I explained it that the chaos gods were interested in the players skill and dedication, not how they used the gods gifts to get out of situations.