The rarity of Strength of the Demon Stone Set is Mythical, and been equipped it takes a “Bundle” slot. At this moment the item is available for trade.
Strength of the Demon Stone Set is a skin for Earth Spirit. The skin was added to the game on January 22, 2014, it was created by bounchfx.
Strength of the Demon Stone Set has been recently added to the game, which makes it rather popular with the game community.