Valakut, the Molten Pinnacle

• WWizards of the Coast2009-10-01
  Official Ruling
  You target a permanent or player when the ability triggers. You decide whether to have Valakut deal damage to that permanent or player as the ability resolves.
• WWizards of the Coast2009-10-01
  Official Ruling
  If a Mountain you control leaves the battlefield between the time Valakut's second ability triggers and the time it resolves, be aware if that was the Mountain that caused Valakut's ability to trigger or not. If it was, Valakut's count isn't affected; if it wasn't, Valakut's count goes down by one.
• WWizards of the Coast2009-10-01
  Official Ruling
  If multiple Mountains enter under your control at the same time, Valakut's second ability could trigger that many times. Each ability takes into consideration the other Mountains that entered at the same time as the one that caused it to trigger.
• WWizards of the Coast2009-10-01
  Official Ruling
  Valakut, the Molten Pinnacle's triggered ability has an "intervening 'if' clause." That means (1) the ability won't trigger at all unless, at the time a Mountain enters under your control, you control five or more Mountains other than that new one, and (2) the ability will do nothing if you control fewer than five Mountains other than that new one by the time it resolves.

Rulings via Scryfall

• WO
  Wizards of the Coast2015-02-03

  Valakut, the Molten Pinnacle was unbanned in modern on February 3, 2015. Recent Modern tournaments have been diverse, with no deck dominating the metagame. We wanted a card that would not easily slot into an existing top deck and also wanted to enable a deck with a different play pattern than the current top decks. Valakut, the Molten Pinnacle was selected as the card to unban. Source: https://magic.wizards.com/en/news/arcana/brief-history-modern-banned-list-2015-02-03
• WO
  Wizards of the Coast2015-02-03

  Valakut, the Molten Pinnacle 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 Coast2012-09-20 · edited

  Valakut, the Molten Pinnacle was unbanned in modern on September 20, 2012. Recent Modern tournaments have been diverse, with no deck dominating the metagame. The DCI is unbanning a card to see how that affects the format, looking for one that would not easily slot into an existing top deck and would enable a deck with a different play pattern. After examining the options, Valakut, the Molten Pinnacle was selected as the card to unban. Source: https://magic.wizards.com/en/news/feature/september-20-2012-dci-banned-restricted-list-announcement-2012-09-20