Eithne is a villain in the Neopets franchise. In Neopets Puzzle Adventure, she first appears to be an ally to the player. However, after the player clears the catacombs of Sakhmet and gets the fire ward lying there, Eithne betrays and attacks the player in an attempt to steal this ward. After a battle against her, another Fire Faerie named Nuria appears and, after some dialogue, Eithne flees the scene. Nuria soon reveals that Eithne is once again working with Tura-Kepek to awaken and control a fiery being named Moltenus, just as she did in the Neopets Mystery Island Volcano plot. The player faces Eithne again at the rim of the volcano on Mystery Island. After losing to the player again, Eithne jumps into the volcano in an attempt to protect the ward she'd been guarding and she hasn't been seen again since.
Personality-wise, Eithne is depicted as cunning and deceptive as well as rude and selfish.
Some might assume Eithne died in her attempt to protect the fire ward, seeing as she jumped into the volcano to do it. However, seeing as she's a Fire Faerie, it can also be assumed she survived.