The rarity of Whisper of the Tribunal is Mythical, and been equipped it takes a “Bundle” slot. At this moment the item is available for trade.
Whisper of the Tribunal is a skin for Silencer. The skin was added to the game on April 21, 2014, it was created by Kramol'nik.
Whisper of the Tribunal has been recently added to the game, which makes it rather popular with the game community.