Obscure D&D Lore

Dungeons & Dragons has been around for 40 years now. As you can imagine, both the roles and the fluff (lore) of D&D have changed a lot during that time. Some fluff remained pretty constant throughout all edition (the difference between arcane and divine magic), some got tweaked between editions (alignment), and a few were radically changed (OD&D's Gnolls and 4e's Eladrin ). This short list isn't going to be too surprising to veteran players but there are some tidbits here that are interesting.

-Gnolls were originally Gnome/Troll hybrids.

-The Gold Dragon was originally the only Lawful (i.e. Good) dragon in OD&D. The remaining five dragons were Chaotic (i.e. Evil) and correspond to what would later be referred to as the Chromatic Dragons.

-There was a UK-published adventure where D&D unofficially crossed over with Warhammer Fantasy. To paraphrase: "In a distant land, the men do not worship the same deities as us . . . they bow to a pantheon of Hope, Anger, and Love . . . and those who will not worship these deities they execute." Hope, Anger, and Love are what Warhammer's Tzeentch, Khorne, and Slaaneesh are embodiments of.

-At one point during AD&D 2e, Yeenoghu (variously the god of Gnolls or the demon prince of Gnolls) was identified as a god of the Giants, and a Giant himself.

-The AD&D 2e multiverse was created by two supergods cosmic snakes who are/were the most powerful beings in the multiverse. 

-In AD&D 2e, Archons (Lawful Good celestials), Asuras (Chaotic Good celestials), and Aasimon (angels) are the transformed souls of Good creatures in the afterlife but Guardinals and Eladrin are actually extraplanar races whose origins have no ties to mortal souls.

-Adding to the above, Asuras, Guardinals, and Eladrin are not immortal like Archons and Aasimon. They do live for a long time though. Guardinals seem to have the shortest lifespans of the three.

-OD&D and Chainmail Gnomes are just Dwarves that live in hills instead of mountainous areas.

-In AD&D 2e, Stygia (one of the Nine Hells) has "ancient tentacled gods" frozen underneath the ice. These descriptions seem to reference the art in Planscape that showed an "evolved" Nupperibo (minor devil) and an "ancient Baatorian" (the inhabitants of the hells before devils moved in).

-In D&D 3.5, probably based on the lore above, Zargon from the Basic D&D module B4 The Lost City was retconned into being an ancient Baatorian despite the fact that the concept had been discarded by the tail end of AD&D 2e.

-Wizards of the Coast created a campaign setting for AD&D 2e based on wuxia. It was only released online (with each chapter as a separate PDF), regarded as crap, and was never again mentioned by WOTC.

-The Witch, an AD&D arcane spellcaster class created by Gary Gygax and published in Dragon Magazine, could not effect clerics, Djinni, or Efreeti.