Echidna

Echidnas are powerful snakegirls which mostly live as dungeon bosses in trap-filled ruins. They use the dungeons to serve as proving grounds for their mates, as those men who can defeat all their snares and subordinates are presumed to be prime breeding material. Echidnas can sense men - even children - with hero potential inside them, and if they find such a male outside their dungeon they may take it upon themselves to train him into husband material.

They are few in number because of their odd reproductive ability: as "Mother of Monsters", only one of their daughters is an echidna, while the rest are different monster species.

Echidnas are revered as gods by snake cultists, and their monsterization rites provide one way that the blue serpents' numbers can increase. However, as echidnas are the most powerful monsters of the lamia family, it can take decades of ritual snake-sex to accrue the demonic energy needed to convert a human woman. In Fallen Maidens and Fallen Brides, Mersé Dascaros is converted directly into an echidna by lilim monsterization, courtesy of Deruella.

Encyclopedia Entry
A type of lamia having the upper body of a woman with bluish skin, and the lower body of a snake. Their magical power is among the highest of all monsters. There are differences in personality depending on the individual but what they have in common is that all of them are extremely lustful. Very few exist, and in most cases, most of them dwell deep within dangerous dungeons, so they hardly ever appear before humans.

The reason they live deep within dungeons is because only superior men can make it there, and they want to have their babies. The dungeons they dwell in are laden with treasures for luring humans, mysterious potions, and the best magical items, etc. They sometimes change into human form using their great magic power. Then they spread information about treasure among humans or request the aid of monster slayers themselves in order to lure superior adventurers to their dungeons. After getting past numerous traps and repelling monsters, once an adventurer reaches the deepest part of the dungeon, he'll find them waiting for him as the final barrier and the reward for clearing the dungeon. Unable to hide their arousal upon finding the one who will become their husband, they'll coil around the body of their beloved man with their snake body, bind him, and go straight for sex. As if to let the man savor their entire body and force him to remember it, they use their entire body including their tits, mouth, and vagina, etc. They give men devilish pleasure that is equal to a succubus, and take them prisoner.

Because it is instinctual for them to accept superior humans as husbands, they can sense the existence of humans who will eventually become heroes. It is said that among the echidna there are some who raised their own men with their own hands before they even showed the slightest potential as heroes, supporting them from the side, helping them grow, and then in the future mating with them, drowning them in pleasure, and taking them prisoner.

Thus the important female supporters of heroes in stories have actually always been echidnas, and it seems in most cases, the heroes who supposedly disappeared and went off somewhere after saving people are actually off somewhere alone with an echidna continuing to have sex.

Out of all the monsters, they have an extremely peculiar nature. Of all the children they ever give birth to in their entire lives, only the first is an echidna, the same as her mother. The children born after that are all varied in race, appearance, and nature, and new types of monsters that have never been born before are also often born. Thus, they are called "the mother of monsters". The reason they seek superior men is to birth even more powerful new monsters.

After getting a husband, and charming him, they devote themselves to baby-making and get pregnant with their husband's children in order to fulfill their desire to give birth to the greatest monsters. Eventually, they'll gently pat their hugely swolen stomach with an expression like a holy mother full of benevolence, and they'll think to themselves "my wonderful child born from my great husband's most delicious semen, how lustful will you be, and how lascivious in appearence? How will you tempt men, and how wild will you go with pleasure?" When a mother of monsters thinks about her child to be born, she naturally smiles.

Trivia

 * The Echidna, also know as the "Mother of All Monsters", is a creature from Greek Mythology. Together with her husband Typhon, the strongest and most feared monster of all, she gave birth some of the most well-known monsters from the Mythos, among which are Cerberus and the Chimaera.