The Skeleton is made out of a magic item that is entirely black. It starts as a gooey oil-like substance in both looks and function. It is nearly indestructible and is an infinite power source. Once it gets hot enough, it hardens, but it retains all its other properties. I have not thought of a name for it, but you are free to suggest. Please do not suggest copyrighted material or a name you were going to use for something personal. There are no benefits in stealing.