I used to think the goddess Nyx of darkness (Greek mythology) was awesome, but not anymore. However, .Nyxi. is just a username I selected because I know it won't get old in a while since it doesn't have to have anything to do with my theme!
Anyway, Dark Lucario sounds simply okay. You obviously like Lucario a lot, but just make sure your obsession won't get old soon. 'Dark' is a good addition to the name, too. XP