This article contains plot details from the latest book.
Frosters are a type of elves with the special ability of cryokinetics. This means that they can manipulate ice particles in the air to freeze whatever they want. In Book 1 of the series, Dex and Marella were tested at Foxfire to see if they may be Frosters. Frosters can also cover themselves in ice as a disguise. This is seen in Neverseen.