Given to you by Melissa Ethelridge, the regeneration potion restores 1 unit of health every second whenever your health drops below 100. It lasts for 6 minutes. You can only use it once, so I suggest you save it, and only pick it up when you're ready for the game's final battle. Melissa is probably the most difficult family member to save, but don't be too bummed out if she dies on you. Just before the final battle, you'll have the opportunity to get a Master Key or skeleton key that unlocks her trunk and gives you access to her special item.