The rarity of Arms of the Onyx Crucible is Rare, and been equipped it takes a “Bundle” slot. At this moment the item is available for trade.
Arms of the Onyx Crucible is a skin for Legion Commander. The skin was added to the game on March 17, 2015, it was created by motenai.
Arms of the Onyx Crucible has been recently added to the game, which makes it rather popular with the game community.