According to Irish folklore, a banshee is a female spirit known for 2 things - her howl and that she warns about impending death. Other than the fact that unless you lift the curse you might die very soon, banshees are rather cool. They're Irish, so they like to drink a lot and have funny accents. The downside is they sing like Christina Aguilera.
A centaur is a half-human half horse. You can imagine where centaurs come from. There are videos on the internet that show a centaur's conception, if you're into shit like that. Centaurs are rather rare nowadays, since cars replaced horses. They can sometimes be found on farms.
A dryad is the soul of a tree. Yup, trees have souls. Since the tree can't move much, it sometimes takes the form of a beautiful woman. If you watched the movie The Guardian from 1990, you probably know that dryads are linked to the tree and if you want to kill the dryad, cut down the tree. If you haven't watched the movie and you want to, don't read the previous sentence because it has a spoiler.
A gorgon is an ancient creature with snakes on its head. It looks more or less human, if you don't count the snakes. The gorgon went extinct centuries ago so we don't know much about them. For example, do they have snakes on their pubic area? Who knows? The most well-known gorgon was Medusa, a butter face killed by Perseus. Although Medusa was repulsing, gorgons can be quite pretty. Oh yeah, they can turn people into stone with their gaze, probably what made humans not like them in the first place and the cause of their extinction.
Harpies are beautiful winged creatures infamous for kidnapping children. They were known for having amazing hair and being cougars, so they were quite popular with the young boys. It was quite easy to tell if a boy was cheating you with a harpy, since they had bird claws for legs and left nasty scars on their lovers' backs. Even though they had wings, they couldn't fly like most birds. Their wings allowed them to move in a jump-like motion. They were also rather harmless, delicate and defenseless. The best proof for that is a jealous girl was able to punch a harpy to death. They went extinct somewhere around the 4th century.
Lamias are female demonic creatures with snake tails instead of legs. They are able to turn full human which is why it's still hard to tell whether or not a girl is a lamia. Even though they have a similar liking to young boys as harpies, lamias aren't very nice since they aren't interested in having sex with their victims (although scientists proved it's possible even in their serpentine form, since snakes have vaginas) as much as eating them. Yes, most lamias eat the boys they seduce, so be careful if you're a boy and suspect your girlfriend to be a lamia. She might be keeping you as rations.
Often mistaken with lamias because of their serpentine tails, nagas are NOT demonic female monsters. First off, they don't necessarily have to be female, since there are both male and female nagas. Secondly, nagas have 4 arms. Even though they were very nice and friendly, people kept taking them as lamias and they went extinct somewhere in Middle Ages.
Also known as ass holes of the seas, sirens are vile creatures that live in the ocean. A typical siren has a wide vocal range and uses their voice to lure sailors. An interesting fact is that it's easy to mistake a male siren with a female siren. This hasn't been brought up too often by the sailors who have encountered these creatures and managed to survived. For obvious reasons. Sirens are often mistaken with undines.
Undines, also known as mermaids, are aquatic people living in the oceans. Unlike sirens, they aren't degenerate rapists. They also don't lure their victims with their voice because they can't actually sing or make any noise with their mouths. They don't have vocal chords. Another peculiar detail about undines is their tail. They have fish tails instead of legs. Undines are well-portraited in the movie Little Mermaid, although there's a lot of bull shit added to the story and mermaid experts don't treat the film as "canon."
Succubi are female demons. If a cubus is male, it means it's an incubus, not a succubus. The succubi are demonic creatures, so it's obvious that they are immoral and like to seduce men for their own gain. They are quite beautiful, despite their demonic features, which include two pairs of horns on their heads, hoofs instead of feet and leathery wings. The wings are used like parachutes when they jump from stone to stone over lava. The most famous succubus is Meridiana, who was the succubus that seduced Gerbert of Aurillac, who later became the pope Silvester II. No bull shit, look it up. There's a book about it.