Lamia

A Lamia is a sort of monster that combines human and snake features, commonly having a human torso from the waist up and a snake body from the waist down. The term naga is sometimes used interchangeably, but they are just as likely to refer to distinct creatures. They tend to share a lot of stereotypical snake traits, like preferring to sneak around and plot rather than fight in the open. An affinity for magic, poison, or hypnosis is also common.

Greek Mythology

The creature known as Lamia used to be the queen of Lybia. She was also the lover of Zeus, which everybody knows how that ends considering who the latter's wife is. Hera, discovering her husband had an affair, did what every ultra jealous goddess did and killed Lamia's children. Oh and then cursed her with insanity and the inability to fall asleep. These two factors caused the queen to mutate over time into a monster with the upper half of a woman and the lower half being that of a snake that would prey and devour children and young men. Zeus, seeing that all of this is something he's to blame for, at least made sure her life won't suffer so much and gave her the ability to remove her eyes from her eye sockets so she would have something that is closest to sleeping.

Dungeons & Dragons

Dungeons & Dragons lamias are totally different from other lamias. Since their first appearance in the Monster Manual for Advanced Dungeons & Dragons 1st edition, typical lamias were described as centaur-like meldings of woman and quadruped beast. Their 2nd edition updated appearance, the Monstrous Compendium volume 2, specifically stated that their lower bodies can resemble goats, deer or lions, among other things - however, as all of the artwork for lamias has traditionally gone with the "lioness-taur" appearance, this has become cemented in peoples' minds as the "true form" of the D&D lamia. Although, strangely, their appearance in 3.5's Monster Manual depicts a male leonic commoner lamia.

However, the iconic snake-girl lamia has also appeared in D&D as well. Called the Lamia Noble, and coming in both male & female forms (males are sword-wielding gishes, females are spellcasters), it appeared for the first time in the Fiend Folio and was later reprinted in typical "subvariant small addition" in the Lamia's entry in the Monstrous Compendium - this lack of artwork for it is probably why few people remember it actually existed. It would not be updated to third edition until Expedition to the Demonweb Pits, late in the game's run-time. The biggest difference from common lamia, aside from the added wizard/sorcerer spells, is that they can shapechange into human form.

Birthright's unique awnsheigh, the Lamia, follows the lion-taur model. A one-time exotic dancer, con-woman, and thief, she accidentally absorbed the tainted bloodline of a man dying on a battlefield when she murdered him to loot the corpse. Years later, after killing and draining several others, she murdered the king of Besaiam and became ruler, constantly funding vainglorious monuments to herself. Her main powers are her ability to instantly charm men, whether with a glance or an aura, and a touch that drains Wisdom and makes men into her fawning servitors. Women are immune to these powers, which is one of the reasons she gets very... catty (hee) whenever pretty ladies are around, the other being that she is envious of her lost human beauty. Between her various charmed puppets, she actually controls a decent-sized holding.

Lamias had their own Ecology Of article in Dragon Magazine #192. According to this article, noble lamias need human mates in order to propagate their species, as interbreeding with each other or with common lamias will only produce more common lamias. Likewise, the common lamias need to mate with humans to produce true offspring, as mating with each other will only produce sa'irs, which are savage beasts that have the forequarters of a goat-horned lion and the hindquarters of a goat... No, you didn't read that wrong; according to Drag-Mag, common lamias, despite looking like women from the waist up, are actually a species of hermaphrodites and so can impregnate and be impregnated as they see fit. Lamias of both "castes" have an annual week-long mating season in summer that drives them wild with lust and sends them looking for human baby-daddies/mommies; a sufficiently attractive human partner could cause them to go into heat outside of this time as well. According to Drag-Mag's statistics, adult commoner lamias are 60% likely to be lion-taurs, 25% likely to be goat-taurs, and 15% likely to be deer/antelope-taurs. Lamia nobles, according to this, can't actually copy spells from scrolls or spellbooks (remember, these were the days before monsters could have classes), so human wizards were especially prized captives.

Traditionally, lamias of all kinds are Chaotic Evil in alignment, being selfish, evil, cruel, lazy hedonists who use their innate ability to drain Wisdom in order to brainwash victims into serving them as slaves, mates and/or food; they don't respect any life other than their own, so the roles are not exclusive.

A variant lamia called a "Tigerus" is native to the Kingdoms of Kalamar 3.5 setting, making its appearance in the setting's personal monster manual, "Dangerous Denizens: The Monsters of Tellene". Unlike common lamias, these are a neutral-aligned species of tiger-taurs who live a stone-age style primitive lifestyle (to put this in perspective, cooking meat is a new and exotic idea for them, though quickly catching on). They lack the Wisdom drain of standard lamias, instead focusing on melee combat (pouncing and raking special attacks), and they sport druidic spells that make jungle life easier, like Speak With Animals, rather than the standard sorcerer powers.

4th edition is an outlier in this regard, as its "lamia" has absolutely no relation to the model portrayed here and which it returned to in 5th edition. Instead, its "lamia" is a species of carnivorous scarab-like beetles native to the Feywild with a voracious appetite for fey flesh (although they'll eat humanoids if they can get them). Their standard hunting MO is to eat the poor bastards alive from the inside out, hollowing out the corpse so they can wriggle under the skin and use the skeleton to move the bug-bag corpse around as a disguise. This lets them get closer to fresh victims. Although this is an awesomely creepy monster idea, its poor choice of name alienated a lot of fans and so it's gone unused since.

Although it's not technically a Lamia, the Marilith Tanar'ri does look like someone fused an Amazon with a Lamia, gave her multiple arms, and then called it a day and her a demon. Likewise, the Lillend is a Celestial who looks like someone slapped wings on a lamia bard and dubbed her an angel.

Pathfinder

Pathfinder's lamias are pretty much exactly the same as their D&D ancestors; the biggest change-up was the creation of the "Lamyros" subtype. Having a family of "lamia-kin" allowed Pathfinder to not only bring back the Lamia Matriarch, but also add some new members to the family -- these first appeared in the original Rise of the Runelords adventure path, but were tweaked when it got reprinted in compilation form under Pathfinder's "new" ruleset.

The Harridan is an elite Lamia, the only creature more important in their loosely-held society than a Lamia Matriarch. It's essentially a giant lamia with added divine spells, and was tweaked to a template only available to lamias with 10+ levels in a divine casting class in the compilation. This "remake" version does state that it's possible to encounter Noble Lamias turned Harridans, but it's very rare, and most are the typical leonic tauress.

The Hungerer is a result of Karzoug experimenting on Harridans in his fleshwarping pits, creating a horrifically disfigured, gaping-mawed, obscenely obese monstrosity that suffers endless pain & hunger, causing it to devour anything and everything around it.

Finally, the Kuchrima is the bottom of the lamia totem pole, being a hideously ragged-looking humanoid vulture that serves as a scout and, more eagerly, garbage disposal; noxious cannibals and gleeful scavengers, these carrion-eaters carry huge bows they use with their prehensile feet from the air and carry foul diseases up close in melee.

A 3rd party netbook, Kobold Quarterly #23, includes unofficial rules for playing a "classic" snake-woman Lamia in Pathfinder or D&D 3.5 in the form of the Lamia Commoner species. It has the following racial profile:

+2 Strength, +2 Charisma, –2 Intelligence: Lamia commoners are physically strong and manipulative.

Medium: Lamia commoners are Medium creatures, and have no bonuses or penalties due to their size.

Normal Speed: Lamia commoners have a base speed of 30 ft. They have a climb speed of 20 ft and a swim speed of 20 ft.

Darkvision: Lamias can see in the dark up to 60 ft.

Low-Light Vision: Lamias can see twice as far as humans in dim light.

Intimidating: Lamias receive a +2 racial bonus on Intimidate skill checks due to their frightening nature and appearance.

Lamian Immunities: Lamias get a +2 racial bonus to saves against mind-affecting spells and effects.

Snake Body: Lamia commoners have neither feet nor legs and thus cannot be tripped. They may not use magic items requiring the feet slot.

Skilled: Lamias receive a +2 racial bonus on Bluff and Use Magic Device checks.

Spell Resistance: Lamias possess spell resistance equal to 5 plus their class levels.

Spell-Like Abilities: A lamia can cast charm person and ventriloquism each 1/day, using her total character level as her caster level.

Weapon Familiarity: Lamia commoners are proficient with the scimitar.

Languages: Lamias begin play speaking Common and Draconic. Lamias with high Intelligence can choose any additional bonus languages, with Abyssal being the most typical.

Vampire: The Masquerade

In Vampire: The Masquerade, the Lamiae are a supposedly extinct bloodline of vampires named after their founder, Lamia. Lamia was the high priestess of a cult of Lilith, and claimed to be her daughter, when the Cappadocian vampire Lazarus found her performing rites to Lilith and proceeded to embrace her. As she changed to a vampire, she had a vision of Lilith who told her about her and her new clans future, and upon awakening, and Lazarus explaining her condition to her, she whispered a couple lines to her sires ear who then promptly ran the fuck away and begun actively avoiding her.

From there she made her way to her clan, and there created her bloodline named after her. They served as the bodyguards and warriors of the Cappadocians and continued the worship and rites of Lilith as their sire had. They mainly consisted of women, as they were seen to be closer to Lilith, who had greater power when compared to their male counterparts, and had a variant of the necromancy discipline based on the four humors. Their weakness was that they carried the Seed of Lilith, a viral disease similar to the black plague that infected those they fed from, with women having a greater resistance to it than men, that would kill those fed from after a few days. If another vampire drank from the same person a lamia had drank, they would become carriers of the disease.

When Augustus Giovanni diablerized Cappadocius, he also supposedly diablerized Lamia, which caused the painful kiss of the Giovanni. The bloodline then became a target for persecution and the other clans worked with the Giovanni to destroy them, with the last Lamia having been killed in 1718... However, at the time of the Final Nights, a group of female vampires calling themselves the Lilin who have the same practices as the Lamia and claims of heritage sprung up in Cairo, leading some to speculate that the bloodline survived.

The Clans of Vampire: The Masquerade
Camarilla							Camarilla Bloodlines

Brujah	Gangrel	Malkavian	Nosferatu	Toreador	Tremere	Ventrue	Daughters of Cacophony	Gargoyles
Sabbat					Sabbat Bloodlines

	Lasombra	Tzimisce			Ahrimanes	Blood Brothers	Harbingers of Skulls	Kiasyd
Independent Clans					Fallen Clans

Assamite	Danava	Setites	Giovanni	Ravnos			Cappadocian	Salubri
Bloodlines

Anda	Azaneali	Baali	Children of Osiris	Lamia	Lhiannan	Nagaraja	Noiad	Samedi	True Brujah
Mixed Heritages

			Antitribu	Caitiff	Panders
The Antediluvians
Absimiliard - Augustus Giovanni - Arikel - Cappadocius - Ennoia - Haqim - Ilyes Lasombra - Malkav - Saulot - Set - Tremere - Tzimisce - Ventru - Zapathasura
Caine

Warhammer: Age of Sigmar

In the new Warhammer: Age of Sigmar game, part of the Daughters of Khaine faction is a race created by Morathi called the Melusai, who are basically Warhammer lamia; female dark elves from the waist up and giant snakes from the waist down. That's all we know about them so far.

Monstergirls (and biology issues)

To get the elephant in the room out of the way, yes, vorarephiles get a serious kick out of these due to snakes swallowing their prey whole. But as for the rest of us...

One problem with Lamia monstergirls that they have in common with Merfolk and Centaurs (despite it being much more rarely discussed with Lamias compared to the other two for some weird reason) is that if they're a nonhuman animal from the waist down, where's their vagina? This might not seem like a problem at first, until you learn that a snake's cloaca is at the base of their actually-very-short tail.

In fact they have a lot of the same problems in this area as the Centaurs and Merfolk each do individually, without any of the easy solutions presented by either. For example, for reasons pertaining to blood distribution, the heart would need to be in the snake part rather than the human part (or at best near where the two parts meet), meaning that placing their junk at waist-height (length?) would give them a uterus wedged between their lungs, esophagus, and trachea (and bringing squirting into the mix would lodge the bladder in there as well), and the problem gets magnified when you take pregnancy into account. Making all their organs of the above-waist human variety would be the equivalent of taking a normal human and giving them legs many times longer (and thus with many times more body mass) than said human organs are equipped to support.

You might be thinking that just putting their junk where a snake's is would be the simplest approach, after all it shouldn't be too hard for her to bend her tail up to meet my dick, right? Well yes, but it still has complications of it's own. Making those genitals human ones would A) look retarded and B) result in lamias of both sexes having to drag their junk along the ground when they slither, and even if you sigh and accept having to stick your dick in an unsexy reptile cloaca there's still the issue of modesty; what the heck sort of clothes could they wear down there that they wouldn't just slither out of the instant they started moving?

Oh well. At least they should all be able to deepthroat any penis with ridiculous ease...

Monstergirl Encyclopedia

In the Monster Girl Encyclopedia, the lamia was one of the first mamono to get her own profile. They are characterized both by their love of using their coils to hug their mates and by their possessiveness; lamia do not let their men go once they choose them, and before KC retconned out any and all "dark" content, they would actually kill their husbands if they dared to cheat on them.

Other branches of the lamia family tree, aside from the Basilisk and the Medusa, include:

Apophis: A cobra lamia from the not!Egypt region, named for the serpentine god of evil in Egyptian mythology, that uses her aphrodisiac, mind-controlling venom to conquer territories to rule over.
Echidna: A powerful lamia variant that can give birth to almost any form of mamono besides its own, who create elaborate dungeon complexes in order to lure skilled, powerful adventurers to claim as their husbands. Takes its name from the Greco-Roman "Mother of Monsters".
Shirohebi: A white-colored lamia variant from Zipangu, a surprisingly shy and docile lamia mage skilled in water elementalism, who tend to serve as clerics to "Ryu", the Zipangu dragon-girl species. They're still as possessively jealous over their husband as normal lamias, though. Take their name from a famous Chinese/Japanese folk story involving a white snake who turned herself into a human and fell in love with a human man. Still retains the ability to use flames from the story but they are instead used to bind the man to become dependent only on her instead of using it to roast said man alive.
Bunyip: A fluffy lamia variant that inhabits rivers, they suffer from such crippling shyness that they completely lose the ability to speak around guys they like, until eventually they get so overheated with lust all they can think to do is pounce on him and coil him up for mating.

Notable Lamias

Ssen Patrick, protagonist of Lamia Daughter Quest.
Miia, the first non-human main character of the "Daily Life With Monstergirls" manga (and also the first member of the main character's unwanted harem).

Gallery

A traditional lamia mating dance.
The 4e monster that temporarily borrowed the name. No, she's not wearing those beetles, the beetles are wearing that eladrin skin.
Technically, she's a Yuan-ti Malison, but can you tell the difference?
There's a snake in my boot!