The rarity of Belt of the Drowning Trench is Mythical. At this moment the item is available for trade.
Belt of the Drowning Trench is a skin for Tidehunter. The skin was added to the game on September 2, 2015, it was created by Godzy.
Belt of the Drowning Trench has been recently added to the game, which makes it rather popular with the game community.