Following the major Magic: The Gathering announcements at the 2019 The Game Awards, Wizards of the Coast has announced a Magic: The Gathering Arena "After Party" event in the game, and it's called "Ashiok vs. Elspeth".
The free event that runs from December 12-16 lets players preview the upcoming cards from Theros Beyond Death, and the format is preconstructed singleton, so you can choose to run the Ashiok deck or the Elspeth deck. The event also lets players use three iconic cards from Magic's history, including "Black Lotus", "Sol Ring", and "Sword of Ice and Fire".
Unfortunately, you won't be able to keep the cards in the event decks in your collection, but you can win Theros Beyond Death in-game boosters for winning a game (max of 3 wins). This is a fun way to preview the new cards before they will officially be released next month. While "Black Lotus" probably won't be legal in any formats available in Magic Arena anytime soon, it's amusing to see the most expensive MTG card get featured in the game.
As the official trailer reveals, it looks like the two planeswalkers are central to Theros Beyond Death's story. MTG Arena is also offering two different preorder bundles for the upcoming set, and each comes with a special planeswalker sleeve featuring Ashiok or Elspeth. If you order both, you can get a pet. Check it out:
Theros Beyond DeathMagic: The Gathering