The rarity of Hat of the Jolly Reaver is Mythical. At this moment the item is available for trade.
Hat of the Jolly Reaver is a skin for Pudge. The skin was added to the game on May 16, 2017, it was created by katzeimsack.
Hat of the Jolly Reaver has been recently added to the game, which makes it rather popular with the game community.