The Collector’s Cache in Dota 2 is available through the Compendium of The International, and it is available for those that purchase the Compendium. If you have it, you will also have a 1 of 250 chances of winning the Immortal Faceless Rex Courier. Only available until the end of the International in Seattle. They will not be available for trade, so
Opening a Collector’s Cache also gives you several ways to increase your Compendium level. The first time you open a Cache will earn you 2 levels, when you open 5 Caches you’ll earn 5 levels, and you’ll earn 11 levels when you open 11 Caches. There’s also a chance that a Cache will contain an item that grants 11 Compendium levels. Additionally, each set from the Collector’s Cache can be recycled for two levels. The Faceless Rex is fully usable and you can use it in trading.