Rudolph Pet

Rudolph Pet was the 21st tier of the Main Event in the Christmas Event 2019, and the event page confirms that tier. It is a legendary reward, and because the event ended long ago, the only route to it today is trading.

The pet is a brown reindeer with large brown antlers and a bright red nose. The wiki says it resembles Rudolph, the red-nosed reindeer, and that is where the name comes from. The wiki's infobox calls it simply Rudolph, while the page title is Rudolph Pet.

That distinction matters because Christmas events produced more than one reindeer pet. Mr. Reindeer, a rare reward from the Christmas Event 2020, is described by the wiki as the third reindeer-related pet released in the game, which fits with Rudolph arriving a year earlier. Both share the brown reindeer base idea, but Rudolph is the one with the bright nose and big antlers.

There is no unbox chance, ability or price listed for it. The confirmed details are the event, the tier number, the rarity and the look.