Wizards of the Coast has made another off-cycle Pioneer ban and restricted announcement today with a couple of changes: "Oko, Thief of Crowns" and "Nexus of Fate" are banned.
The metagame for the new nonrotating format featuring cards from Return to Ravnica and onwards has a more balanced metagame recently thanks to the banning of three cards earlier this month. However, two decks proved to be outliers, according to WotC, and they are Simic Food Ramp and Simic Nexus.
"Over the past weeks, Simic Food Ramp has had a nearly 60% non-mirror match win rate on Magic Online and has earned more than twice as many 5–0 league finishes than any other archetype," R&D developer Ian Duke said. "It has favorable matchups against most of the other top decks and no strongly unfavorable matchups."
"In considering possible changes to bring the deck in better balance with the rest of the field, Oko, Thief of Crowns stands out as a powerful threat that is difficult to answer and shores up many natural weaknesses of ramp decks," Duke added. "In addition, Oko, Thief of Crowns appears in several of the other strongest decks and would likely continue to contribute to metagame balance problems long term. Therefore, we are banning Oko, Thief of Crowns."
The next update on Pioneer will be on Monday, January 6. WotC will plan to sync up Pioneer updates with the rest of their B&R updates but there won't be any scheduled B&R announcements.