[Scoop?] Libris Mortis: The Book of the Undead, from WotC

[Wayside]

Wayside has the right of it here, although shouldn't it be the genitive plural mortuorum to denote possession, rather than the ablative plural?

You're absolutely right. It's cool how I noted that the adjective needed to be used substantively, then proceeded to put it into agreement with a noun anyway . The genitive in this case is descriptive though, not possessive.

Now that I think about it, I'd bet that there's precedent for using mortuus collectively in the singular. That would give you a way around the sometimes dissonant (to English-speaking ears at least) Latin plurals with libris mortui.