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.¹
The muck claims a hundred living things for each meager treasure it spews forth.
Illus. Greg & Tim Hildebrandt

Crystal Keep Rulings Summaries

• Affects lands tapped for rest of turn, not just swamps in play at the time it resolves. [Urza's Destiny FAQ 1999/05/25] This is because it affects players and not the lands themselves. [DeLaney 1999/06/13]
• Affects lands that count as a swamp. For example, if you tap Badlands for {R}, it will produce an additional {B}. [Urza's Destiny FAQ 1999/05/25]

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