Because Sygni are born with an Earthian physical form, tapping into the immense forces of Arweinydd-based magic can have detrimental effects on the Sygni's body and mental state. Legends tell of Sygni who fell into madness, becoming twisted by their inability to withstand the flow of both Chaos and Creation. These became Dark Sygnus, also known as Darkstar.
Luccious is the only Dark Sygnus recorded since the Time Before. He was not a naturally-born Sygnus, but was developed using Zerom's essence combined with Earthian essence to purposely create a creature with Sygnus-like power.