One of the more natural things to appear in the early issues of Alarums & Excursions is a certain degree of fluidity between the concepts of monsters and player characters. This is one of the things that Gygax initially encouraged in the text of OD&D, saying that a player can be pretty much any "type" described in the game, but that was played down quite vehemently in the DMG, with a prolonged essay on humanocentrism that has stuck with the Gygaxian mode of play for decades. I don't disagree with its main thrust, in that I feel that the majority of PCs should be human, but it did change the overall direction of the game, particularly in drawing a hard line between PCs and monsters.
Early A&E issues were very heavy on the actual play stories, and one of the characters with a lot of stories under her belt was Brilliant Jade, a fox spirit (a fox who turns herself human, taken from Chinese myth). This is interesting to me for a few reasons. One, the lycanthrope was actually pretty thoroughly covered in the early A&Es, frequently as a player type and not specifically a monster so much. Two, the concept was freely borrowed from myth and inserted without a lot of world-building or fantasy mythologizing around it. You had fox spirits in myth, therefore they were relevant in D&D. Three, the boundary between player and monster types was very deeply fluid.
A couple of other examples should suffice for what I mean. A number of writeups include the fact that monsters were given character levels, this long before 3e made it standard. Hobgoblins could be 6th level Fighters just as well as humans. As time went on and more statistics were printed in the zine, monster writeups often included a full experience chart with multiple levels detailed out. I really like the implications of this, because it lets you come up with monsters that are really varied and unique.
It's interesting that this method, which seems to have fallen by the wayside for AD&D in favor of simply adding to the variety of monsters, was embraced most in 3e, where it allowed for nigh-infinite fine tuning of opponents. With OD&D, it's radically different. Since the system is so much simpler, it's possible to do this much more easily. The example that brought me to realize that this was an early phenomenon was a reference to an "F6 Hobgoblin," who would have 6 levels as a Fighting-Man. 6 HD, possibly better AC from armor, hits as a 6 HD monster. This seems to me like a simple way to make a lot more out of a small inventory of traditional monsters, and just the sort of thing one would expect of the time before there were dozens of books full of monster statistics. Definitely something that will find its way into the lower works of my dungeon.