|“||Stheno, the Bargain Mart was a front! You’re going native! Now, put down that ridiculous tray and help me kill this demigod.||”|
On the quest through The Labyrinth, Tyson urged Briares to summon his brothers to help the unprotected Camp Half Blood. Briares told Tyson, Percy, Annabeth, and Grover that his immortal brothers did not exist anymore. Percy then recalled that Medusa's sisters were, also, forgotten immortals and they passed on.
Euryale, along with her sister Stheno, had been repeatedly killed by Percy, but they just kept on reforming because Thanatos was unable to prevent monsters from coming back from the dead. She was determined to take revenge on Percy for vaporizing Medusa, who hadn't reformed yet. She scolded her sister for telling Percy the secret of Gorgon blood and for being too obsessed with her work.
Euryale was far more narrow minded than Stheno and crueler. She appeared to be the dominant sister as Stheno seemed nervous when she began to shout for not following her plans, and she always ordered Stheno around. Euryale was also smarter than Stheno but not more than Medusa.
- According to Medusa in The Lightning Thief, Euryale and Stheno had both faded, yet, they appear in The Son of Neptune, meaning Gaea may have some way to bring back even faded beings.
- Her name is pronounced like Muriel.
- A genus of waterlily and species of bat are named after her.