A new Black Library book coming out soon titled Beastgrave will include three Underworld cards with new Black Library Exclusive artwork. The cards are not new, so this isn't a I must by the book to get these cards. So not necessary but a cool new way to cross promote their products!
via the Warhammer Community
"These cards first appeared in Warhammer Underworlds: Nightvault – so they’re still usable in competitive play – and are themed around Katophrane Tomes, the preferred reading matter of the former lords of Shadespire. Check out just what their favourite books were with this exclusive first look at the new art."