- "I knew your mother both before and after the Change took her. She was ugly before and, let me tell you, there was little difference afterward. Your mother was so ugly that even magic mirrors would not talk to her. Your mother was so ugly, she-"
- — Hel, taunting the Sphinx about her mother
Echidna (sometimes called the "mother of all monsters") is an Elder whose body was severely warped by the Change. She is the Wife of the Great Elder Typhon, with whom she mothered several famous monsters, such as the Sphinx, the Hydra, Gorgons, Cerberus, and the Chimera. She does not personally appear in the series.
Like most Elders, Echidna's once-humanoid appearance took on animal-like qualities as she aged in a process called the Change. She grew a long serpentine tail, draconic wings, and her hair transformed into a writhing mass of living, venomous snakes (similar to a Gorgon).
- Immortality: Echidna is Immortal and does not age. Though an immortal may be poisoned or slain in battle, they may live for thousands or millions of years.
- An echidna is an unusual egg-laying mammal, similar in appearance to an anteater, that shares a common ancestor with the modern platypus. The animal is named after the Greek depiction of Echidna, since the animal has both mammal-like and reptile-like traits.
- Hel noted to the Sphinx that Echidna was hideous even before the Change.