Drought

Enchantment    (CMC:4)

During your upkeep, pay or destroy Drought. Before a spell that requires as part of its casting cost may be cast or an ability that requires as part of its activation cost may be played, the controller of that spell or ability sacrifices a swamp for each in the spell's casting cost or the ability's activation cost.

IA • ENNéNé Thomas

™ & © 1993—1995 Wizards of the Coast

Legal in: Ice Age Block,Legacy,Vintage,Commander

Oracle Text (click to copy):

10/4/2004
You have to sacrifice a Swamp for each black mana in the activation cost. If you use Pestilence with , that's 4 activations with  each so you sacrifice 4 Swamps.
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 and will have colons in their reminder texts.