Jades are Lurkers. Their method of consumption involves dissolving their prey's insides and drinking them, like spiders.
They look human, but when they turn into the monster (or "go Jade"), their appearance changes: their eyes are red slit pupils on black, their lips and tongue turn black, their nails curve out into thick claws, and their teeth transform into wider, sharper, shark's teeth. One is born to be a Jade. The trait descends through the female line in the family.
Jades apparently have a sweet tooth.
Candy is a Jade. She's taking a potion made first by Kinski, then by Allegra, to keep the Jade part of herself under control. She can trace all of her Jade ancestors back to the First Crusade.