Cheapest priced copy (Mystery Booster 2): $4.99 at Card Kingdom, near mint, their price list as of .
Contamination 
Enchantment · Rare · Urza's Saga · #123
At the beginning of your upkeep, sacrifice this enchantment unless you sacrifice a creature.
If a land is tapped for mana, it produces {B} instead of any other type and amount.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
3 printings · $4.99 to $39.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mystery Booster 2 | 178 | Rare | $4.99 | $39.99 |
| The List | USG-123 | Rare | $8.49 | — |
| Urza's Saga | 123 | Rare | $16.99 | — |
3 rulings from Wizards of the Coast
- 4 October 2004The second ability of this card is a replacement effect, not a triggered ability.
- 4 October 2004You choose whether to sacrifice a creature or not on resolution. If not, then you sacrifice Contamination. You can choose to not sacrifice even if you no longer control Contamination on resolution.
- 4 October 2004External effects that generate more mana still generate their additional mana as directed without being affected by this card. Effects which generate more mana based on what type of mana the land produces will be affected in color but not in amount.