no setup, explanation, or introductions
There
is setup though, the discovery of the petrified crowd, their "resurrection" (turned out it was more like freeing them up), and his intent of using them, were all shown. And we do get an introduction for Marie, just in
the previous chapter. And the way
she gets announced in the preceding half-chapter does carry (in hindsight) an implication that there could be more of her fellow uncursed coming.
And it's all pretty fitting in this whole arc of uncovering some of the empire's frightful past, terrible secrets, and hidden capabilities.
This is stuff that needed to be shown to us before it mattered to the plot.
Can't say I really agree. But I'll concede there's a limited amount of times the author can pull this off before the readers feel like they're just looking at a succession of asspulls.
But really, "everything MUST have been exposed/foreshadowed" might be an absolute rule in detective stories, but I don't think it really holds in other genres. Especially here where it often seems that the primary genre is humour rather than adventure.