Lingering Injuries: With this rule, character can suffer long-term or permanent injuries. This rule is actually intended to reduce the lethality of the campaign, which sounds paradoxical but bear with me. I suggest that the condition for incurring a lingering injury is the following: the first time a character would die either 1) because of massive damage, or 2) because of three failed death saving throws, the character will instead suffering a lingering injury. The second time a character would die, the character dies as normal even if they have recovered from a previous lingering injury.
Note the above conditions. Some effects will kill a character outright if they reduce the character’s HP to 0, e.g., via decapitation or disintegration. Such effects will result in death as normal, rather than a lingering injury. A decapitation will not result in survival with a broken leg instead, for example. Death by exhaustion does not result in a lingering injury and instead results in death.
There are nine different Lingering Injuries your character could suffer, which range in severity from scars and severe wounds to lost limbs or a lost eye. Most of these injuries require significantly powerful magic, i.e 6th level spells such as regenerate to recover from.