Death

Many dangers can lead to death. They are detailed below.

Instant Death from Damage

Massive Damage can kill you instantly. When damage reduces you to 0 Hit Points and there is damage remaining, you die if the remaining damage equals or exceeds your hit point maximum.
For example, a cleric with a maximum of 12 hit points currently has 6 hit points. If she takes 18 damage from an attack, she is reduced to 0 hit points, but 12 damage remains. Because the remaining damage equals her hit point maximum, the cleric dies instantly.

Death Saving Throws

When you are reduced to 0 hit points, you gains a level of Exhaustion and fall Unconscious.
Whenever you start your turn with 0 hit points, the GM will roll a special saving throw, called a death saving throw, to determine whether you creep closer to death or hang onto life.
Unlike other saving throws, this one isn't tied to any ability score. You are in the hands of fate now, aided only by spells and features that improve your chances of succeeding on a saving throw.
The GM rolls a 1d20 in secret. If the roll is 10 or higher, you succeed. Otherwise, you fail. A success or failure has no effect by itself. On your third success, you become stable. On your third failure, you die. The successes and failures don't need to be consecutive; the GM will keep track of both until you collect three of a kind. The number of both is reset to zero when you regain any hit points, thereby becoming stable.
Since the GM rolls your death saving throws in secret, you never know just how close to death you really are -- while hovering on death's door, getting your character aid is an urgent priority!
Rolling 1 or 20. When the GM rolls your death saving throw and rolls a 1 on the 1d20 , it counts as two failures. If they roll a 20 on the 1d20 , you regain 1 hit point.
Damage at 0 Hit Points. If you take any damage while you have 0 hit points, you suffer a death saving throw failure. If the damage is from a critical hit, you suffer two failures instead. If the damage equals or exceeds your hit point maximum, you suffer instant death.

Death from Unavoidable Injury

Some injuries and Conditions are critical enough to kill a creature outright without dealing damage. For example, certain magical weapons can cause automatic decapitation. Suffocating can lead to death without injury. Exhaustion can lead to death.
For a mortal character, these injuries and conditions result in automatic and instant death.

Monsters and Death

Most of the time, monsters die the instant they drop to 0 hit points, rather than falling Unconscious and making death saving throws.
Mighty villains and special nonplayer characters are common exceptions; the GM might have them fall unconscious and follow the same rules as player characters. Adjudicating the death of non-player characters is at the sole discretion of the GM.