Bubbling Muck

Sorcery, B (1)
Until end of turn, whenever a player taps a Swamp for mana, that player adds {B} to his or her mana pool (in addition to the mana the land produces).¹
The muck claims a hundred living things for each meager treasure it spews forth.
Illus. Greg & Tim Hildebrandt

Gatherer Card Rulings [Nov 2009]

• 10/4/2004: Affects lands with type Swamp, not lands that are named "Swamp."
• 10/4/2004: Affects lands tapped for rest of turn, not just swamps on the battlefield at the time it resolves. This is because it affects players and not the lands themselves.

Format Legality	Legal in Vintage, Legacy Banned in Extended, Standard, MTGO Classic
Printings (1/6)	Urza's Destiny (Common)