The First Fantasy Campaign: Monsters

The final section of JG 37 "The First Fantasy Campaign" lists a number of monsters, apparently drawn from Chainmail, for which additional descriptions are provided.  My guess is that these predate OD&D, and may have been used in preparing the Guidon manuscript.

Dragons:

Table of dragon types, presumably based on those mentioned in Chainmail (note the inclusion of "purple" dragons, and the lack of gold dragons).  Percentage given is the % "in lair" when encountered.

The first edition of Chainmail describes red dragons (based on Smaug from "The Hobbit") and also lists white, black, blue, green, and purple (each of which were described previously by Gary Gygax in the "Diplomacy" fanzine Thangorodrim (see OD&D Dragons: On the Origin of Species).

The chance for any type of dragon to be found asleep in its lair is given as 80%, in which case a "free chop" is permitted.  There is also a % chance of talking and rules for encountering mated pairs, which were probably incorporated into the OD&D description.

Finally, there are rules for capturing or "subduing" a dragon, which were likewise probably incorporated into the OD&D description.  Richard Snider expanded upon these rules in his additions (see Richard Snider's Additions: The Dragons).

Orcs:

The five tribes of orcs mentioned are those appearing in Chainmail (Orcs of the Red Eye, Orcs of Mordor, Orcs of the Mountains, Orcs of the White Hand, and Isengarders).  Descriptions of their fortified villages are similar to that found in the OD&D description.

Bandits:

Bandits are not mentioned in Chainmail, and so much of Arneson's description might have been used as the basis for the entry in OD&D.

Nomads:

Nomads are not mentioned in Chainmail, and so much of Arneson's description might have been used as the basis for the entry in OD&D.

Trolls and Ogres:

Trolls and Ogres appear under the same category in Chainmail.  Some additional details are provided regarding their vulnerabilities and lairs.

Wights (and Ghouls):

Wights and Ghouls appear under the same category in Chainmail.  Some additional details are provided regarding their paralysis attack and lairs.  Energy drain is not mentioned, but appears in Richard Snider's Additions.

True Trolls:

Are differentiated from normal trolls, as in Chainmail, and certain details regarding their treasure is provided.

Rocs:

Rocs are mentioned in Chainmail, although Arneson provides additional details regarding their nests and the value of their eggs and flightless fledglings,

Tarns:

Tarns, which appear in John Norman's Gor series, are described as the same as Rocs, but larger in some cases (War Tarns, Cargo Tarns, and Racing Tarns are described).

Basilisk:

Basilisks are mentioned in Chainmail, although Arneson provides additional details regarding their treasure when encountered in lairs.

Balrog:

Balrogs are mentioned in Chainmail, although Arneson provides additional details regarding their treasure when encountered in lairs.

Giants:

Giants are mentioned in Chainmail, although Arneson mentions that they "carry their wealth with them and vary in size".