Cheapest priced copy (Eldritch Moon): $0.39 at Card Kingdom, near mint, their price list as of .
Campaign of Vengeance 
Enchantment · Uncommon · The List · #EMN-182
Whenever a creature you control attacks, defending player loses 1 life and you gain 1 life.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.39 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Eldritch Moon | 182 | Uncommon | $0.39 | $1.49 |
| The List | EMN-182 | Uncommon | $0.39 | — |
3 rulings from Wizards of the Coast
- 13 July 2016In a multiplayer game, each instance of the ability affects only one defending player. For example, if you attack player A with two creatures and player B with two creatures, each of those players will lose 2 life, not 4.
- 13 July 2016In a Two-Headed Giant game, Campaign of Vengeance’s triggered ability has one defending player of your choice lose 1 life. The team doesn’t lose 2 life.
- 13 July 2016If a creature attacks a planeswalker, the defending player is the player who controls that planeswalker.