Text (SM+errata): ~this~ deals X damage divided as you choose among any number of target creatures and/or players, where X is the number of Mountains you control as you cast ~this~. [Oracle 2009/07/08]
It counts the mountains that the time you announce this spell and pay the cost. This value is locked in and doesn't change after that. [Shadowmoor FAQ 2008/04/21]
If you control no mountains, X is zero and you pick no targets. [Shadowmoor FAQ 2008/04/21]
You X is greater than zero, you must pick between 1 and X targets. Each target must be assigned at least 1 damage. [Shadowmoor FAQ 2008/04/21]
