Regeneration (5e Variant Rule)
From D&D Wiki
Regeneration is the ability to regain lost hit points every turn. While this is straightforward for monsters, it works a little differently if you are a Player Character. Unrestricted regeneration would remove the need for Hit Dice: you would just take a short rest to recover all your hit points. Clearly some modification is required. Therefore this rule allows a player to effectively spend their Hit Dice in advance to create a pool of hit points from which regeneration is drawn.
- When you have the regeneration trait, you draw on a pool of regeneration points to regain hit points at the start of your turn.
- When you first make your character, and at the end of each long rest, you can spend any number of your Hit Dice. For each Hit Dice spent, roll the die and add your Constitution modifier to it. You gain regeneration points equal to the total.
- At the start of your turn you spend regeneration points as specified by the trait that grants you regeneration. You regain an equal number of lost hit points. Excess regeneration points are retained. You lose unused regeneration points when you generate a new pool at the end of a long rest.
Regeneration and Death
If massive damage would normally kill you instantly, and you have regeneration points left and are able to regenerate, you remain alive but unconscious. When you regenerate at the start of your turn, instead of regaining hit points, the remaining damage is reduced by the same amount. When the remaining damage is reduced to 0 you regain consciousness.
If at any point you are at 0 hit points and are unable to regenerate, then you are truly slain.