The rarity of Frostheart is Uncommon, and been equipped it takes a “Bundle” slot. At this moment the item is available for trade.
Frostheart is a skin for Winter Wyvern. The skin was added to the game on August 31, 2016, it was created by Toasty.
Frostheart has been recently added to the game, which makes it rather popular with the game community.