The rarity of Stormwrought Arbiter is Mythical, and been equipped it takes a “Bundle” slot. At this moment the item is available for trade.
Stormwrought Arbiter is a skin for Sven. The skin was added to the game on April 28, 2016.
Stormwrought Arbiter has been recently added to the game, which makes it rather popular with the game community.