City of Shadows | Magic: The Gathering
Formats City of Shadows is Legal in
Official Oracle Text for City of Shadows
: Add to your mana pool, where X is the number of storage counters on City of Shadows.
Official Rulings for City of Shadows
10/1/2009 : You can activate City of Shadows's second ability while it has no storage counters on it, though it won't add any mana to your mana pool in this case. You've still tapped it for mana, though, in case any abilities (such as the ability of a Fertile Ground enchanting it) care about that.