The rarity of Flight of the Valkyrie is Rare, and been equipped it takes a “Bundle” slot. At this moment the item is available for trade.
Flight of the Valkyrie is a skin for Legion Commander. The skin was added to the game on March 11, 2014, it was created by Jeremy Klein.
Flight of the Valkyrie has been recently added to the game, which makes it rather popular with the game community.