Her face and torso are that of a beautiful woman and was depicted as winged in archaic vase-paintings, but always with the body of a serpent.
the goddess fierce Echidna who is half a nymph with glancing eyes and fair cheeks, and half again a huge snake, great and awful, with speckled skin, eating raw flesh beneath the secret parts of the holy earth. And there she has a cave deep down under a hollow rock far from the deathless gods and mortal men. There, then, did the gods appoint her a glorious house to dwell in: and she keeps guard in Arima beneath the earth, grim Echidna, a nymph who dies not nor grows old all her days. (Theogony, 295-305)
Echidna also had many children with her mate, Typhon, all of which were horrible monsterous creatures earning her the name "Mother of Monsters".
She was killed by Argus, Hera's Watchman
Her children included…
Nemean Lion
Lycian Chimera
Ladon
Theban Sphinx
Lerneaen Hydra
Cerberus
Orthrus
Ethon/Caucasus Eagle
Teumession Fox
Crommyonian Sow
Colchian Dragon
There is also a mammal native to Australia that was named after this fierce mythical being.