Siege of Towers | Magic: The Gathering
Formats Siege of Towers is Legal in
Official Oracle Text for Siege of Towers
Target Mountain becomes a 3/1 creature. It's still a land.
Official Rulings for Siege of Towers
8/1/2008 : 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 his or her most recent turn. It doesn't matter how long the permanent has been a creature.