Booting up Magic: Arena will pull up a brand new banned list, which now includes the extremely contentious Oko, Thief of Crowns planeswalker that was just introduced in the most recent set of cards: Throne of Eldraine.
Oko was an extremely oppressive card that could get out as early as turn two (with help), and set the tempo for the rest of the game. Pro players were essentially building around Oko or against him, as the entire meta was completely dominated by that one card: to the point where roughly 70% of some championship events included Oko in every deck. That reign ends today, as Oko is banned in standard play in paper form and in Magic: Arena.
But he's not the only banned card! Veil of Summer and Once Upon a Time are banned as well, on top of the existing recent Field of the Dead ban. In a statement, Magic overseer Wizards of the Coast stated that "the standard metagame has been in an unhealthy state," and they are addressing "green's general dominance" in the meta by banning the two aforementioned cards on top.
There's no grace period for this in Arena: those cards are banned right now and you cannot play with them, though you will receive wildcards for them based on how many copies you own. Tabletop play is scheduled to ban the cards on November 22. You can find the full ban list below.
Welp, I only had one Oko deck, but several of my builds included Once Upon a Time (man, Gruul was so powerful with it in the meta). I'll be making adjustments posthaste!
Banned and Restricted announcement [Wizards of the Coast]