Dropping to 0 Hit Points

When a creature drops to 0 Hit Points, it either dies outright or falls unconscious, as explained below.
Instant Death

Falling Unconscious
If you reach 0 Hit Points and don't die instantly, you have the Unconscious condition until you regain any Hit Points, and you now face making Death Saving Throws.
Death Saving Throws

Stabilizing a Creature

Monsters and Death
Monster Death. A monster dies the instant it drops to 0 Hit Points, although a Game Master can ignore this rule for an individual monster and treat it like a character.