Imagine having a metabolism that is so fast that you would be able to eat whatever you and how much you want without gaining an ounce. Shrews and hummingbirds are real life examples of this because their metabolisms are so fast that they have to constantly eat in order to live. I am thinking of giving this trait to one of the main characters in my sequel spin-off to serve as a primary weakness since their metabolism will be infinitely faster than either a shrew or hummingbird. It will be more of a double-edged sword in the sense that they will have regenerative abilities, but they would have to keep eating in order to fuel themselves. Without a consistent supply of food to sustain them, they would be severely weakened to the point of death.