A single Preview Crate: Frost Atronach will be a possible reward as part of the December 2019 daily rewards, given for logging in for 21 days that month. Unlike regular Frost Atronach crates, the Preview Crate pulls from a limited pool of potential rewards. They can be distinguished from regular Frost Atronach crates by their grey color, as opposed to the usual brown.
Notably, these crates are guaranteed to grant one of five pets modeled after the Apex-level mounts of the Frost Atronach Season released the following month. The pets found in the preview crates are not available in regular Frost Atronach Crates.
The possible rewards are as follows, grouped by rarity with Legendary rewards being the rarest:
Duplicate Legendary rewards grant from extraction.33
Unwanted Fine Rewards grant from extraction.1
Unwanted Common Rewards grant from extraction.1