The rarity of Stygian Maw is Rare, and been equipped it takes a “Bundle” slot. At this moment the item is available for trade.
Stygian Maw is a skin for Shadow Demon. The skin was added to the game on October 26, 2017, it was created by Ethan Patterson.
Stygian Maw is currently one of the most popular skins, but it is rarely seen in the game due to its high price.