Gumiho

Gumihos are legendary nine-tailed fox creatures who, when disguised in humanoid form, use charm and guile to lure prey deep into the forest before revealing their true form and striking. The green-eyed canids use brutally sharp fangs to tear out their victim's throat and feast on their liver. Those few who survive a gumiho's trap recall the canid's eerie green eyes as well as a strange marble amulet warn around the monster's neck.

Old stories claim that a fox transforms into a gumiho once it has lived for a thousand years, quadrupling in size, growing eight additional tails, and gaining the power to change shape. Terrifyingly, it also gains an insatiable hunger for the livers of people. This hunger is so closely connected to a gumiho's power that if it abstains from eating liver for one thousand days, the gumiho loses its magic and permanently takes on its humanoid guise-also losing its evil nature in the process.