Empty Swamp

Pay 1 Life: Add {b} to your mana pool. Use this
ability only once per turn, only on your turn.
Pay XX Life: Add {b} to your mana pool. X is
equal to the number of mana produced by this
land so far this turn. Use this only if this land
has already produced mana this turn.
Empty Swamp does not tap for mana. Do not
untap Empty Swamp o during your untap step.