I spent two days rewriting and expanding the explanation of this spell, now the longest spell page on my wiki:
What a headache ... and long overdue, though it's not the first time I've decided to increase the amount of detail. This is one of those bits of AD&D that left way too much up to the DM's fiat, meaning that the exact benefits of the familiar was never available to the player in any real sense. What exactly does "night vision" really mean?
Unfortunately, some of the needed back up links are still unavailable, as they need to be written, notably the pseudo-dragon and the quasit. All I can say is that while the latter might be something like the original, the pseudo-dragon definitely won't be. I've never understood the point in introducing a small dragon that's in no way like a dragon, and assuming the prefix "pseudo" is an effective handwave. In any case, those monsters haven't been created because I have a LOT left to do. They'll get done when I need them, or when they happen to come up.
I added six additional kinds of lesser familiar; obviously, I could have added more, as virtually anything could be one. I considered "rabbit" but I'm not convinced on that one yet. I marginally advanced the powers and knowledge conferred on the caster by the familiar and narrowed the gap considerably between what a lesser familiar can bestow and what a greater familiar can. I think it's important for players to want every familiar for some reason, so that it's not just a lottery of winning big or getting the booby prize. Personally, I'll take a chameleon, dog or mongoose quite happily. I think the monkey needs one more small benefit, but I'm worn down by making this spell fit into the sage system and other parts of the game, and I can't think of something.
Anyway, have a look. It's technically a first draft, so there are probably spelling errors and the occasional missing word. Feel free to point them out.