The rarity of Big 'Un is Uncommon, and been equipped it takes a “Bundle” slot. At this moment the item is available for trade.
Big 'Un is a skin for Alchemist. The skin was added to the game on August 31, 2016, it was created by katzeimsack.
Big 'Un is currently one of the most popular skins, but it is rarely seen in the game due to its high price.