Treasures can be opened to find cosmetic items or sets. Treasures are obtained through the item drop system, charms, or bought directly from the Dota 2 Store. Each treasure can be opened once, and can contain a few different items.
Each treasure comes with a list of Standard drops, as well as Very Rare drop(s). Some treasures also contain Extremely Rare drop(s), often an Unusual courier, which occur at approximately 1-2% chance. Item rarity does affect drop chances.
Opening several of the same treasure will guarantee a different item will be received each time. This rule does not apply to Very Rare or Extremely Rare drops. After all standard items have been received, future treasure openings will yield random items from the droplist.
Some treasures, such as 37 - Ancient Scroll Case, always drop multiple items.