VAMPIRES: Vampires first appeared in OD&D, and most of the changes presented here are clarifications to their already-existing abilities. There are plenty of those, so strap in, this could take a while.
The first change to be noted is that vampires are now Chaotic Evil. In OD&D's three-alignment system, they were Chaotic. In the article that first introduced the expanded nine-point alignment system (from The Strategic Review #6) Vampires were said to epitomise Lawful Evil, but that's not the case in the Monster Manual.
As before, it is said that vampires must rest in a coffin during daylight hours. This requirement is now lessened for vampires who are far underground, though they still need to rest in a coffin occasionally, as their power is restored only by contact with soil from their own grave. It's all very Dracula, but I wonder about the specific use of the term "grave". What if a vampire was never buried? What soil do they require then?
It's noted that vampires, and all other undead, exist simultaneously in the Material and Negative Plane. I'm pretty sure that this has been mentioned in the Monster Manual before, but it's been a while since I started this whole thing and I can't remember.
Vampires are now explicitly said to have a Strength score of 18/76, bringing them in line with the uncanny strength they usually have in stories. The damage done by a vampire's blow has been altered to reflect this. An 18/76 Strength gives a damage bonus of +4, and a vampire's attack now deals 5-10 damage. or 1d6+4. It's lovely when D&D makes sense.
As before, a vampire drains two levels from its victim with every hit. Deal with it. They are still only hit with magical weapons, and their regeneration ability remains unaltered. As before, when reduced to 0 hit points a vampire is forced into gaseous form. This is expanded on here: the vampire must then return to its coffin within 10 turns and regrow its body over the course of 8 hours.
Vampires get a number of new immunities: the standard things that don't work on undead (sleep, charm, hold), poison, and paralysis. They are also given resistance to spells based on cold or electricity.
Some other abilities that have been barely altered: turning into gaseous form at will, transforming into a large bat, a gaze that can charm a person, and the ability to summon rats, bats or wolves. The summoning has been clarified. Bats can only be summoned when underground. Rats and bats do not attack, but merely confuse and obstruct vision. Summoned creatures take 2-12 rounds to arrive.
As before, vampires will recoil from garlic, a mirror, or a lawful good holy symbol if any of these is strongly presented. Again, this is clarified. These objects can't be used to drive a vampire away. Garlic only causes them to hesitate for 1-4 rounds. With the other two, a vampire will try to position itself so that the object isn't between itself and the victim, or it might try to get a minion to deal with the problem.
(Note: the cross is specifically mentioned here as a lawful good holy symbol, further evidence of the Christian roots of the D&D cleric. I have to decide at some point whether I will have a Christian church in my campaign, or if I'll assign the cross to an existing Greyhawk deity. Probably the latter.)
The same three methods for killing a vampire in OD&D are given here as well: exposure to direct sunlight, immersion in running water, and a stake through the heart. Guess what? There are more clarifications! Sunlight now takes a full turn to kill a vampire, but that vampire loses all of its powers during that exposure. Immersion in water drains a third of the vampires hit points every round, thus killing it in three rounds. A stake through the heart now only keeps a vampire dead for as long as the stake remains lodged in its chest. To permanently kill a vampire in this way, it must be beheaded, and holy wafers must be stuffed in its mouth. (So there's another bit of Christian iconography. Whichever Greyhawk church I assign the cross will have to get holy wafers as well, I guess.)
Holy water is now said to deal 2-7 damage on a vampire struck with it.
As in OD&D, any human or humanoid killed by a vampire becomes a vampire under the control of the original (which means demi-human vampires are a thing. And goblins, and orcs, and maybe even ogres and giants. Rad!). Clarifications!!! The new vampire is said to be "appropriately-strengthed." I suppose that means Hit Dice? It's specifically said here that vampires can have character classes, and that a vampire cleric will be Chaotic Evil. No word on what happens to a vampire druid or paladin; I imagine that either would lose their powers. The transformation into a vampire now takes one day after the creature is buried, but if it isn't buried it does not occur (that answers my grave dirt concerns from earlier). If the head vampire is killed, all the rest become free-willed. (This would have made the ending of The Lost Boys a lot messier.)
Finally, we see the introduction of the eastern vampire into D&D. They are the same as regular vampires, except that they are invisible. In exchange for this they can't charm with their gaze, and can't assume gaseous form at will (presumably they still do so when reduced to 0 hit points). I wonder about the invisibility. The way it's worded makes it seem more like a permanent state than an ability they can use. I would probably play it as an ability, and treat it like the spell; level-draining monsters that can't ever be seen? No thank you.
Stat Changes: Number Appearing: Old - 1-6, New - 1-4; Armor Class: Old - 2, New - 1; Hit Dice: Old - 7 to 9, New - 8+3; Damage: Old - 1-10, New - 5-10
Just one monster today, folks. This one took a while, but it does cover the entirety of the letter V. Progress!