In Creating Life, we discussed both animals and monsters, so these won’t be covered here, but we can take any of them and add supernatural elements.
We don’t always need to decide where a creature originated, but it helps us determine everything else we need to invent for it. Under circumstances we invent, predetermined sources of energy can give rise to this creature. Having decided where such energy is available helps us establish a physical point of origin. How and even if our creature relocates can also add believability. Does it need a new habitat due to the way its body now functions? Perhaps it can’t abide certain temperatures or other environmental issues, or just craves a specific environment now and adapts its habitat accordingly.
The creature’s physical properties and capabilities are often linked, though they needn’t be. What changes can we make to its appearance based on its supernatural abilities? Perhaps there are marks on the skin that react to external stimuli. That said, it can be advantageous to have this creation externally indistinguishable from the source; that allows for surprises when they prove to be other than they appeared. Decide on whether this subterfuge is helpful. If not, pair the skill to the body, such as ears that can move in odd ways because their hearing is superior, or eyes that look different (color, pupil shape, etc.) because their vision is altered.