Regeneration

You don't know what strange mutation has caused this, but you are good at healing much faster than other humanoids. You gain the following effects. 

• You regain 5 hitpoints per round passively. You can boost this to 10 hit points per round if you burn your action and bonus action.
• You cannot be healed by healing spells; healing potions only heal half as much rounded down. 
• If you are brought to 0 hitpoints, once per long rest, you will heal to 10 at the end of the next round if you are not damaged for a full round. 
• If you are brought to 0 hitpoints again, you will automatically fail your first two death saves at your turn on each round. 
• You take double damage from fire and acid.