The rarity of Ethereal Monarch is Mythical, and been equipped it takes a “Bundle” slot. At this moment the item is available for trade.
Ethereal Monarch is a skin for Puck. The skin was added to the game on September 14, 2016, it was created by Zipfinator.
Ethereal Monarch is currently one of the most popular skins, but it is rarely seen in the game due to its high price.