Valve released the Treasure of the Venerable One to celebrate Singles' Day 2017. The treasure is discounted by 20% during this weekend, prior November 13.
With the November 10 update a new treasure chest has been introduced in Dota 2: the Treasure of the Venerable One.
It contains sets for ten different heroes - the Fervid Monarch for Viper is the only rare drop. Until November 13, you can buy it from the Dota 2 store for $1.99 instead of $2.49.
Treasure of the Venerable One’s hero sets
Buying nine treasures before November 13 will also give you a free bonus chat emotion bundle: the Autumn Sale Emoticon Pack.