The rarity of Egg of the Vermillion Crucible is Mythical. At this moment the item is available for trade.
Egg of the Vermillion Crucible is a skin for Phoenix. The skin was added to the game on January 10, 2017, it was created by Dr. Robo.
Egg of the Vermillion Crucible has been recently added to the game, which makes it rather popular with the game community.