The rarity of Helm of the Volatile Firmament is Uncommon. At this moment the item is available for trade.
Helm of the Volatile Firmament is a skin for Spectre. The skin was added to the game on August 14, 2014, it was created by GreyskyS.
Helm of the Volatile Firmament has been recently added to the game, which makes it rather popular with the game community.