Is the basis for whether a mob is a worthy foe (for Fray Dice, etc.) the hit dice of the whole mob, or the hit dice of the constituent creatures? My gut says the former, but I haven't found a ruling one way or the other.
It’s the latter. In the descriptions of the mobs it says composed of 1 HD creatures and subject to fray dice and effects that target such (paraphrasing mine).
+Marshall Brengle Ah, it's in the stat blocks! I was looking at the general mob rules only. Thank you!
+Robert Wiesehan it’ll say composed of 1 HD creatures, 2 HD, etc.