SPHINX: As far as I can tell, this is the first mention of sphinxes in D&D, aside from the Egyptian Mythos in Supplement IV: Gods, Demigods & Heroes. That version is super-duper-powerful, on a scale far above those presented in the Monster Manual, so I'm going to chalk that one up as a sphinx demi-god, and treat these ones as brand new monsters.
ANDROSPHINX: These are the standard male versions of the sphinx, and probably the most powerful of the four varieties, both because of their stats and because they can cast spells as 6th-level clerics. In addition they have a magical roar that they can use three times a day. Each of these roars is increasingly powerful: the first causes fear, the second causes paralysis and deafness, and the third causes temporary strength-loss and can also knock creatures down and stun them. Larger creatures tend to be resistant, and of course there are saving throws. Regardless, the androsphinx has to be progressively angrier to use each one.
The only tidbit about them outside of combat that we get is that they resent female sphinxes for being so damned smart and neutral, and they tend to avoid them. I kind of hate these guys already.
CRIOSPHINX: No, not an ice sphinx despite the name, these guys are neutral with ram-heads. They have no special powers, but they do seem like a seedy lot, extorting travellers out of treasure and lusting after female sphinxes. They may not have much going on mechanically, but just those two traits give them a little something to hang an identity on.
GYNOSPHINX: These are the females, and the smartest of the bunch. Though they have a lot of knowledge, they also prize wealth, and only help people who pay them. This is a decent enough adventure hook to be going on with, but in a lovely touch it's also said that they will accept payment in the form of poetry, prose, knowledge, or "the location of an androsphinx". Hooks galore! Even better, if payment isn't made the gynosphinx will just eat the offender.
In addition to some pretty good stats (it's an 8 Hit Die monster), gynosphinxes can cast the following spells once per day: detect magic, read magic, read languages, detect invisible, locate object, dispel magic, clairaudience, clairvoyance, remove curse, legend lore, and any of the symbol spells.
HIERACOSPHINX: Evil, hawk-headed sphinxes that live in hilly regions. They love treasure, and eating warm-blooded creatures, particularly humans. There's not a lot to distinguish these guys from a whole bunch of other monsters in the Monster Manual, to be honest.
Spiders, giant or otherwise, have a spotty history thus far in D&D. They're mentioned as possibilities in the catch-all Animal categories in D&D Vol. 2. Phase Spiders have appeared in Supplement I: Greyhawk, and Water Spiders in Supplement II: Blackmoor. And of course they showed up in the ubiquitous Wilderness Encounter Tables from Supplement III: ELdritch Wizardry. But regular spiders, and generic giant spiders have not had a proper stat block thus far in D&D.
Apparently spiders are found everywhere except in the ice, but charmingly there are legends of giant, white fur-clad spiders from the polar climes. I'm creeped out already.
GIANT SPIDER: Giant spiders lurk in webs, laying in wait to ambush creatures with their lethal poisonous bites. Their webs are tough to break out of (1 round for Strength 18, 2 rounds for Str 17, and so on), and they can't be burned away. These spiders will flee from superior foes, and I'm struck by their Chaotic Evil alignment and Low intelligence. If anything, they seem like an attempt to model the spiders from The Hobbit, who were intelligent and quite nasty. At Size L, though, I think these guys are a lot bigger. I seem to remember the spiders from The Hobbit being around man-size, but I could be wrong.
HUGE SPIDER: Huge spiders don't build webs, instead hunting prey down and leaping on them (or perhaps hiding themselves like trap-door spiders). They are very good at gaining surprise, and they also have poisonous bites (albeit the victim gets a +1 on their save). They're about man-size, but only as smart as your average animal.
LARGE SPIDER: These spiders are about as large as a halfling, with no special abilities beyond wall-crawling and a weaker poisonous bite (the victim gets a +2). I wouldn't want to meet one, but most seasoned adventurers should be able to handle them without any trouble. (Hang on, though, the Number Appearing is 2-20. That could get ugly.)
PHASE SPIDER: As mentioned before, these awful bastards first appeared in Supplement I: Greyhawk. Unfortunately they have not changed here at all; in fact, with stronger poison and the addition of webs they're even more dangerous. As before, their primary ability is to shift out of phase with their surroundings when "attacking or being attacked", which makes them basically unhittable. I guess they can be attacked when not phased, but when would that be? If they can phase when being attacked, it's a moot point. There are ways to target them (the phase door spell, oil and armor of etherealness), but they're not all that easy to come by. To top it off, victims of their poisonous bite suffer a -2 penalty on their save, and they have webs like a giant spider. These guys are deadly.
Number Appearing: Old - 1-6, New - 1-4; Armor Class: Old - 6, New 7; Hit Dice: Old - 5, New - 5+5
WATER SPIDER: Water spiders were in Supplement II: Blackmoor, but those were sea spiders, and these are specifically said to live in fresh water. Otherwise they're the same, living in underwater air pockets built amidst vegetation, snatching passing prey and killing it with poison. The only addition is that they are often on friendly terms with nixies, as these spiders are somewhat intelligent.
A rare salt water species is mentioned at the end of the entry, supposedly twice the size of the fresh-water variety; that fits the details of the version from Supplement II, which gives me a lovely warm glow inside. I like it when things match up like that.
Number Appearing: Old - 1-12, New - 1-10; Movement: Old - 6", New - 15"; Hit Dice: Old - 4 to 6, New - 3+3
SPRITES: Sprites are a difficult monster to pin down in OD&D. They were present in Chainmail, named as sprites; the original D&D boxed set states that these sprites were actually pixies, a form of air sprite. It also adds in nixies (water sprites) and dryads (tree sprites), so it seemed there that sprites were more of a category than a creature in their own right. Dryads, nixies and pixies all appear in the Monster Manual, as does the sprite itself.
To be honest, sprites aren't spectacularly different from pixies, being perhaps somewhat less magically endowed and somewhat stronger physically. This works well for me, as it matches up well with them being treated as interchangeable entities in Chainmail. They have bows that can cause sleep for 1-6 hours, can become invisible at will, detect evil, and move silently. Here's the interesting part: they are said to "hate evil and ugliness of all sorts". Evil I can understand, it's an actual for real thing in D&D, but ugliness? Sprites are a shallow bunch. They aren't shy about hating evil, either: while they move any good character they out to sleep into a safe place, they will straight-up murder any evil ones. The fate of ugly victims is not specified.
GIANT SQUID: Giant squid were mentioned in passing in D&D Vol. 3, and further detailed in Supplement II: Blackmoor. The version here is about twice as strong as that in Supplement II, so it's basically an entirely new monster (although a larger variety that can constrict like a snake is mentioned in the original entry). It keeps a few of the same traits, such as the armoured body and the softer tentacles and head, and the ability to squirt ink. What it's gained is the ability to constrict with its tentacles, an attack that can only be ended by severing a tentacle or killing the squid. It takes 10 points of damage to sever a tentacle, and these hit points don't count towards the squid's regular hit point total.
There are a lot of changes here, but they're easy to reconcile: the stats from Supplement II are for the younger squid, and these stats are for the full-grown variety. Easy-peasy.
Number Appearing: Old - 2-12, New - 1; Movement: Old - 3"/12", New - 3"/18"; Hit Dice: Old - 6, New 12; Number of Attacks: 6 tentacles and 1 beak, New - 9 tentacles and 1 beak; Damage: Old - 1-8 per tentacle, 1-10 beak; New - 1-6 per tentacle, 5-20 beak