Any combatant that reaches 0 hit points is incapacitated and unable to act. They’re dead if not stabilized within 1 minute or by the end of the fight (whichever is later).

There are thirteen damage types

This group represents damage done by weapons and mundane venom

• Slashing
• Piercing
• Bludgeoning
• Poison

This group represents the elemental damage done by earth, air, fire, and water

• Acid
• Lightning
• Fire
• Cold

This group represents the two poles of angelic and demonic damage

• Radiant
• Necrotic

This final group represents magical energies

• Thunder
• Force
• Psychic

Certain monsters or characters may have abilities which make them resistant to fire damage or vulnerable to acid damage, for example. Each of these essentially acts as a modifier to the total damage taken by that specific type of damage. If multiple types of damage are done, the damage modifier is only applied to the relevant damage rather than the total.

Resistance: The target takes half damage

Vulnerability: The target takes double damage

Immunity: The target takes zero damage

Whenever you start your turn with 0 hit points, you must make a special check, called a death check, to determine whether you creep closer to death or hang onto life. Unlike other checks, 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 generic check.

Roll a d20. If the roll is 11 or higher, you succeed. Otherwise, you fail. A success or failure has no effect by itself. On your third success, you become stable (see below). On your third failure, you die. The successes and failures don't need to be consecutive; 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 or become stable.

Rolling 1 or 20
When you make a death check and roll a 1 on the d20, it counts as two failures. If you roll a 20 on the d20, 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 check 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.

Stabilizing a Creature
The best way to save a creature with 0 hit points is to heal it. If healing is unavailable, the creature can at least be stabilized so that it isn't killed by a failed death check.

You can use your action to administer first aid to an unconscious creature and attempt to stabilize it, which requires a successful Medicine check.

A stable creature doesn't make death checks, even though it has 0 hit points, but it does remain unconscious. The creature stops being stable, and must start making death checks again, if it takes any damage. A stable creature that isn't healed regains 1 hit point after 1d4 hours.

Monsters and Death
Most DMs have a monster die the instant it drops to 0 hit points, rather than having it fall unconscious and make death checks.

Mighty villains and special nonplayer characters are common exceptions; the DM might have them fall unconscious and follow the same rules as player characters.

See also HEALING AND INJURY for stabilization and recovery.

Once a character is stabilized, roll on this table to determine any lasting wounds were inflicted by the blows that knocked them to zero hit points.

Copied from 5TD. Should we put death saves back in? The way it is here, it is REALLY hard to kill a PC.

It's really hard, unless no one is able to stabilize them. We could put a stricter time limit, rather than death saves. Maybe 5 turns?

Yes, I suppose you are right about stabilization. I still kind of like the death saves from 5E, though. It keeps PCs who are more or less out of the fight engaged, and it allows bad guys to deliver the coup-de-grace for added assholery. With a 5/10 round timer there is no way to adjudicate that. –AHS