So everybody knows basically what the story of Frankenstein is, but what if instead of making a monster in his lab, he created a dungeon inside a world of fantasy? And inside his dungeon, the only way to heal yourself, is to replace the broken, cut, and/or severed part with something else from a monster, which would then "heal" it.
In other words, if you lost a finger, you would need to replace the missing finger with another body part which you can find from a monster. Dead of alive, it doesn't make a difference either way. It doesn't have to even be a finger. Just as long as the size of where it attaches to is relatively the same. So if you loss your thumb, you can replace it with another thumb, or maybe you choose to use a claw, or even a toe. But you cannot use say, a full leg in that spot, as the connection points have too big of a size difference.
Additionally, if you would like to add parts, a second pair of arms for example, you would just have to have 2 injured spots where they could be attached to. Then they would "heal" to your body, giving you their full range of motion and abilities that they can offer.
You do need to be cautious of which parts are added from which creatures. Give yourself the fangs from a vampire, and you basically turn into a vampire yourself. Meaning that without a renewable source of fresh blood, or if you are standing in direct sunlight, you will not make it for long.
But why would anyone risk entering this dungeon? Because if you make it to the end, you can choose to keep your replaced/added parts, along with a ton of gold and treasure.