"It's the main and purest source of energy in the universe" ~ Arceus
Mystic Energy can be defined as the purest source of energy in Dragon's Paradise Universe.Due to it's propieties and the term "Energy=Mass" it's possible to even create life with it,with the requiered materials.
However since to create energy according to physics a group of particles must be divided to generate heat and thus energy.And as it's name suggest it uses a similar principle.Since the energy reached a pure state it must come from a very pure product, and that's the aura.Aura is burned constantly to produce this energy, however the Aura must be from a clean soul,body and mind to be perfectly pure.Many creatures in DP Universe can't use Aura but instead have acces to many powers,this is thanks to the mystic energy.Unafortunely for the beings called Dragon Master this is more curel, since they agreed with Arceus to become a Dragon Master and achieve immortality and a huge quantity of power is thanks to this.
Dragon Masters can manage the Mystic Energy directly,not for example Dialga who converts it into Time Waves used to use various attacks.However Aura itself isn't as pure as a Soul.So to obtain this Energy directly a Dragon Master Soul must be burned constantly.It is a fair trade,since a Dragon Master potential is even greater than Arceus.However if a Soul is consumed the body would wander as an empty shell.So instead the "Soul Particles" that were burned get corrupt and serve as fuel to generate greater energy.
When Enough "Soul Particles" are burned the Dragon Master Mystic Energy starts to get corrupted due to the fuel and finally drives it insane since it Soul no longer belogs to it.To prevent it a Dragon Master must complete tasks and defeat demons to make Arceus use their souls to burn their "Soul Particles" and restore the Dragon Master Soul.In other words, to prevent corruption a Dragon Master must kill demons.
The way Msytic Energy works is as follows: First of all the metabolism of the body changes completely.Since the main source of energy for the entire body is "Soul Particles" they are burned outside the person in the Soul Range and the skin cells absorb the Mystic Energy,while other cells mantain it in the Soul Range.The Energy goes directly into the blood and makes a complete change where the Blood Cells take Mystic Energy instead of just Oxygen to the point the cells are called Mystic Cells.These cells carry the Mystic Energy and the plasma containing them is now formed of Liquid Mystic Energy and since it is almost invisible and the fact Mystic Cells get atracted to the body it makes it look like a Dragon Master doesn't have blood.The Energy is supplied to the rest of the body,specially the Brain,the stomach and the muscles because thanks to the energy a Dragon Master cannot die because it's cells regenerate very fast when a wound appears.However since the cells can barely take such huge amounts of energy and now they are also capable of dividing the person"Soul Particles" there are formed 7 identical organs all around the body where it is regulated the Energy send to various organs.A Dragon Master can never have any kind of disease, however corruption at high levels it is almost like a death-guarantee to the Dragon Master.