Dropping to 0 Hit Points

When reduced to 0 hit points, a creature falls unconscious and suffers one level of exhaustion.

Coup de Grace: The creature suffers another level of exhaustion each time it takes damage while at 0 hit points. If the source of that damage is the attack of an adjacent foe, the creature dies instead.

Waking Up: The unconsciousness ends when the creature regains any number of hit points. If the creature regains no hit points, it awakens with 1 hit point after D4 minutes.

Instant Death: When damage leaves a creature with 0 hit points and there is damage remaining, the creature dies if the remaining damage equals or exceeds its hit point maximum. If the source of that damage is a melee attack, the attacker can choose not to inflict instant death. The GM can also decide that special circumstances cause a creature to live or die despite the rules.

While the majority of bad guys prefer to take prisoners, a bloodthirsty Undead monster or a major villain with something to prove will not hesitate to execute your beaten and defenseless hero.