Magic's Commander format see rarely sees bannings of new cards occur, but apparently a recently released card was too much for the format to handle. The Commander RC banned Hullbreacher, which was printed in Commander Legends (see "Wizards of the Coast Unveils a Jeweled Lotus Card for 'Magic: The Gathering' 'Commander Legends'!"). They justified their banning of the card with the following rationale:

"Hullbreacher has been a problem card since its release. Its ostensible defensive use against extra card draw has been dwarfed by offensively combining it with mass-draw effects to easily strip players hands while accelerating the controller. That play pattern isn’t something we want prevalent in casual play (see the Leovold ban), and we have seen a lot of evidence that it is too tempting even there, as it combines with wheels and other popular casual staples. The case against the card was overwhelming." 

In addition to banning Hullbreacher, the RC went on to clarify how Dungeon cards, from the upcoming Adventures in the Forgotten Realms set (see "Mark Rosewater Teases Cards in Upcoming 'D&D' 'Magic: The Gathering' Set"), work in Commander. Dungeons are specialized process markers that exist in the command zone until completed. These cards can't be inserted into a deck, so the RC updated their rules to make sure card abilities that could bring a card from outside of the game into play couldn't target a Dungeon.