Death Saves
When dealing with Death Saves (depending on the game) the Referee will roll death saves for the players to decrease meta gaming, increase tension, and teamwork. While a player is in this state, the creature will meet the reaper. For every failed roll, the reaper will land a hit and every success will be a miss. This is revealed after either healing or the three successes. Death Saves reset on a short rest or long rests.
Hero Tokens
When a character completely dies valiantly, the player receives one Hero Token for his/her next character. Players can only have one at a time. If an opportunity approaches and that player still has one, it will replace the old one. In the DMG page 264. Hero point(s) (or Hero Tokens in this case) grants a one time use of a d6 to any roll. This includes death saves. You can only have one at a time.
A valiant death, sole survivor, or epic decisions grants a chance of getting a Hero Token.