Image credit: Wizards of the Coast
Wizards of the Coast made their Magic: The Gathering Banned & Restricted announcement today. Unsurprisingly, there are no changes in Standard and Modern; however, in Vintage, two cards have been restriccted, and one was unrestricted. "Restricted" means that players can only have one copy of the card in the deck, opposed to banning, which completely forbids the use of the card in the format.
The two cards restricted are Monastery Mentor and Thorn of Amethyst.
Many blue-based decks use Monastery Mentor as a kill condition, and due to the abundance of powerful zero- to one-mana cost noncreature spells in the format, Wizards is restricting it to allow more diversity when it comes to choosing win conditions.
Wizards was thinking whether to restrict Thorn of Amethyst or Sphere of Resistance. To weaken Mishra's Workshop-based decks that have been dominating the Vintage metagame, they decided to restrict the more impactful of the two. The disruptive card is too efficient at enabling those decks to apply creature-based threats unimpeded.
The one card they unrestricted is Yawgmoth's Bargain.
Powerful draw engines like Paradoxical Outcome and Griselbrand exist in the format, so they considered unrestricting this one. They considered Windfall but ended up choosing Yawgmoth's Bargain as the safer choice.