This is a basic platformer with a game state tied to light. In light, the world is colorful, but draining. In darkness, a black smudge comes after you, gaining speed when you stay in darkness.
Since visibility is not a core factor of the game, the strat is to stay in darkness as long as possible and to flicker the light when the monster gets onto you. The monster will then reset completely.
A simple and competent product. Shoot higher, and come back in January!