Stoneforge Mystic

• WWizards of the Coast2010-03-01
  Official Ruling
  When Stoneforge Mystic's second ability resolves, you may put any Equipment card from your hand onto the battlefield, not just the one you searched for with its first ability. The Equipment is put onto the battlefield unattached.

Rulings via Scryfall

• WO
  Wizards of the Coast2015-02-03

  Stoneforge Mystic was banned in modern on February 3, 2015. Modern kicked off with a banned list that was created in large part based on Legacy play, the old Extended format, and decks played at the Community Cup that year. We are going to allow turn-four combination decks, but not decks that consistently win the game on turn three. Source: https://magic.wizards.com/en/news/arcana/brief-history-modern-banned-list-2015-02-03
• WO
  Wizards of the Coast2019-08-26

  Stoneforge Mystic was unbanned in modern on August 26, 2019. We believe the Modern metagame and power level are in a place where Stoneforge Mystic is now an appropriate inclusion in the card pool. Our hope is that as gameplay becomes less graveyard focused, Stoneforge Mystic serves as an enticing draw for decks to refocus toward the battlefield, creature combat, and card advantage. Source: https://magic.wizards.com/en/news/news/august-26-2019-banned-and-restricted-announcement-2019-08-26
• WO
  Wizards of the Coast2011-09-20

  Stoneforge Mystic was banned in extended on September 20, 2011. To avoid repeating this, the DCI is banning the cards that have been most played in the most successful Standard and Extended decks over the past three years. For reasons similar to why these cards were banned in other formats, the DCI is banning them in Extended. Source: https://magic.wizards.com/en/news/feature/explanation-september-2011-br-changes-2011-09-20-0
• WO
  Wizards of the Coast2011-06-20

  Stoneforge Mystic was banned in standard on June 20, 2011. Stoneforge Mystic is appearing in winning deck lists an alarming percentage of the time, contributing to a "stagnant and unhealthy" Standard metagame. The card is "flat-out too powerful," and the ban aims to address declining attendance and restore format diversity. Source: https://magic.wizards.com/en/news/feature/standard-bannings-explained-2011-06-20-0