Though the executioner did not speak, the villagers got the message.

Public Execution

Destroy target creature an opponent controls. Each other creature that player controls gets -2/-0 until end of turn.

The List

Conspiracy: Take the Crown

Magic 2013

Only creatures controlled by the player when Public Execution resolves will get -2/-0. Creatures that enter under that player's control or that the player gains control of later in the turn are unaffected.

Public Execution targets only the creature it destroys. If that creature is an illegal target when Public Execution tries to resolve, it won't resolve and none of its effects will happen. No creature will get -2/-0.

If the target creature regenerates or has indestructible, each other creature controlled by that creature's controller will still get -2/-0.