Unusual is a quality for equipment that has a special particle effect. Couriers are the only type of equipment that can be Unusual, and can only be obtained at a 1–2% chance through opening certain Treasures.
An Unusual courier's effect is defined by the Ethereal Gem that is placed inside it.
The color of most Unusual effects can be altered by Prismatic Gems.
Unusuals come with one Ethereal socket and one Prismatic socket. Ethereal and Prismatic gems can be extracted with a Master Artificer's Hammer and placed on a different Unusual courier. Using a Master Artificer's Hammer will destroy the original courier. Inserting a new Ethereal or Prismatic Gem will overwrite the current one.