You woke up in a cavern, deep under the overworld. You don't know who, nor where you are. The only thing you know for sure, you died. How did you passed away? You don't know either. As a specter, you can walk freely, even dash in those deep caves.
Now with your ghostly abilities, you can go faster and farther than before, in a blink. Allowing you to cross streams, small chasms etc.
But one danger remains.
Direct sunlight, or bright lights can arm, or kill you if you stay enough in direct contact. But something changed in you, you can now control, possess, the living.
Those small creatures will give you a chance to leave those caves, and maybe discover what caused your death?