Even though it was just introduced this past October, Magic The Gathering's new format, Pioneer, has already had a plethora of cards added to its ban list. For those who don't know, Pioneer acts as a halfway point between Standard and Modern to ease players into the more expanded and crazier field of Modern. Pioneer follows all standard constructed rules but allows every expansion and core set from Return to Ravnica onward.
Today Wizards of the Coast made an announcement adding three more cards to Pioneer's ban list bringing the list up to a total of 12 cards. The new cards added to the ban list are Field of the Dead, Smuggler's Copter, and Once Upon a Time. Pioneer is currently only supported by the tabletop version and Magic Online. Magic The Gathering Arena's new Historic format has already been implemented, so Pioneer is not available in Arena.
These additions come after a series of Pioneer PTQ Tournaments that were held as a part of Magic Online's Pioneer week. Wizards says that, while it is happy with the direction the new format has been heading, some changes needed to be made after data from this first big batch of Pioneer tournaments came in. Smuggler's Copter was banned to curb the effectiveness of aggressive decks, mono black most specifically. Field of the Dead being banned shouldn't be a surprise to anyone, as it has already been banned in Standard due to its overwhelming effectiveness in ramp based decks. Then lastly, Once Upon a Time has also been banned due to being one of the key parts of how oppressive mono-green stompy decks have become across multiple formats, as we saw in the new Magic The Gathering Standard ban list.
Wizards' decision to be more reactive to bans for this new format, as opposed to launching the format with a pre-made ban list, seems to have been successful as it has been able to use real-world data as it becomes available to make more precise and informed decisions. Granted, this has made these early bans very rapid-fire, but once the format begins to settle down, Wizards plans for these bans to be less frequent and be more on the same schedule as other non-rotating formats. If anyone plans to get good at Magic The Gathering, they have to pay attention to factors like this, regardless of what format they play. The next Pioneer ban announcement is scheduled for December 9th.
Source: Wizards of the Coast