Blackmoor is a supplementary rulebook (product designation TSR 2004) of the original edition of the Dungeons & Dragons fantasy role-playing game written by Dave Arneson (with a foreword by Gary Gygax).

The odds of hitting any specific body part changed depending on the character's height and weapon reach.

A number of these underwater monsters and magic items were the creations of Steve Marsh, added to the supplement in order to compensate for material by Arneson left out of the final edit.

[8][9] Following the release of the original Dungeons & Dragons rulebooks, Gary Gygax and Dave Arneson decided to publish expansions of their respective campaigns.

[10] In March 1975, Gygax told a wargaming newsletter that Arneson was working on a final draft, and TSR began accepting preorders for the product and advertised it in The Strategic Review.