Ouroboros Crates (previously called Welkynd Ouroboros Crates) are promotional Crown Crates which can be obtained through Twitch. Unlike Seasonal Crates, they mostly contain consumables, with a low chance of obtaining an exclusive collectible.
The Crates first became available on May 22, 2018. The promotion was originally exclusive to PC/Mac, although a limited number of Ouroboros Crates were also given to console players in July 2018 due to a bug with that month's daily rewards. Since May 11 2019, Ouroboros Crates have been attainable through Twitch on all platforms.