Drought | Magic: The Gathering
Formats Drought is Legal in
Official Oracle Text for Drought
Spells cost an additional "Sacrifice a Swamp" to cast for each black mana symbol in their mana costs.
Activated abilities cost an additional "Sacrifice a Swamp" to activate for each black mana symbol in their activation costs.
Official Rulings for Drought
8/1/2008 : A hybrid symbol that is both black and another type is a black mana symbol, regardless of what cost is paid for it.
7/1/2013 : Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keywords are activated abilities; they have colons in their reminder text.