Blackmoor (Supplement II), softback supplement for Original D&D, 1st printing, by Dave Arneson
The second supplement for D&D. This supplement introduced Monks and Assassins, a hit location system (whatever happened to that?), rules for underwater adventures, diseases, and the Sahuagin. It also includes TSR’s first ever published adventure ‘The Temple of the Frog’.
These copies are first printings, from December 1975.