The "Essence" type is also known as "Raw" or "Pure". The explaination for this type is that all Pokemon have an amount of a strange life-energy known as Essence. However with most Pokemon it is "focused" into something: E.G the "Essence" of a Fire type is focused in such a way that it creates fire and related capabilities, and Electric types generate electricity with their Essence. Essence (creatures) however haven't got focused energy; all they can do is release this pure form of energy in various ways and hope to use it by the sheer force and power behind it.