Collectors arcana: Optional rules from Dave Arneson's Blackmoor campaign. This supplement contained the first published adventure module, Temple of the Frog.
Arneson introduced the sub-classes "Monk" and "Assassin", additional melee rules, and new monsters (Sahuagin!).
Arneson is still gathering his players for at least a yearly session. That makes the Blackmoor campaign the longest-running D&D campaign worldwide.
1st Printing: The first printing is highly sought after by collectors and thus more valuable.
It has the TSR lizard man logo on the cover. There's no printing information given on the first page of the booklet other than the year (1975).
(see picture above).
2nd to 7th Printing: The second printing has the TSR lizard man logo on the cover.
The distinguishing printing information is given on the first page of the booklet.