User blog comment:Dispelling Mage/Chapter: The Hill Extending towards Tomorrow (494)/@comment-5672982-20160721143318/@comment-94.209.1.231-20160721190022

"Maybe God Serena's eighth dragon larcima is a lightning dragon lacrima."

Possible, but what would the difference be? We already know that Purgatory relates to Hellfire. Also, Laxus already has Lightning Dragon Lacrima, so repeating it would be pretty dumb, if not lazy in some way.

"Wouldn't Dark Dragon's magic be darkness/shadows?"

Perhaps. Maybe it could be demon/fear themed, or even deep space/black hole themed. The latter could go nicely with the Star theme if possible. Emotion such as fear could be a thing, and still be unique in a way.

Fear/Doom/Despair Dragon Slayer Magic