"There is no saving this world, not anymore. But we shall be its bloody vengeance."
—Sorin Markov

Campaign of Vengeance

Whenever a creature you control attacks, defending player loses 1 life and you gain 1 life.

The List

Eldritch Moon

If a creature attacks a planeswalker, the defending player is the player who controls that planeswalker.

In 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.

In 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.