Balduvian Frostwaker

• WWizards of the Coast2006-07-15
  Official Ruling
  Balduvian Frostwaker’s effect has no duration. The snow land is a creature as long as it’s on the battlefield.
• WWizards of the Coast2006-07-15
  Official Ruling
  If an affected land later loses the supertype snow, Balduvian Frostwaker’s effect doesn’t end. The land will remain a creature.
• WWizards of the Coast2008-08-01
  Official Ruling
  A noncreature permanent that turns into a creature can attack, and its abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn’t matter how long the permanent has been a creature.

Rulings via Scryfall