A Melodisian Stone is a gem that resides within the heart of all Myumons and is said to be the hidden sound energy of all living beings in the world. Those with musical talent can use these stones to absorb the positive energies of an adoring crowd, where it becomes a crystal of high purity. Presumably, the more energies absorbed by the stone and the purer it is, the more powerful the stone itself becomes in resisting dark music energies.
When a Melodisian Stone is exposed to dark music energy, it becomes tainted with "Dark Melodisian". The more powerful or "evolved" a Melodisian stone, the more dark music energy it takes to taint and darken it. When a stone becomes so tainted with dark energies, the Myumon it belongs to will be morphed into a Dark Monster, and while there is a way to rectify this procedure, it is very difficult as the monster will attack any musically talented Myumon it comes across, including those trying to rescue them. It appears to cause the Myumon who's stone is being corrupted great pain when a monster uses his dark energies on the stone.