[@Noxxis][@Rune_Alchemist][@Guilty Spark]

Personally, I'm more for the idea of missions being the bread and butter of the rp.  Long term arcs and story lines are great, don't get me wrong, but I think for the most part they over complicate things, especially for the GM and cause the rp to burn out much quicker.

As far as dark guilds go, I was thinking of one where the master of the guild got into some dark magic and killed all the members.  Then he placed their souls in puppets.  These puppets are then able to use the magic of the souls and he can ever turn the personality on and off at a whim. So the story there would be the guild master is hunting down powerful mages in order to add them to his 'guild.'

Another idea for a powerful enemy, is a similar vain, is one in the same vain as legion were a single powerful mage went crazy, because he saw something horrible, and his mind split into several distinct personalities, all with magical abilities of their own.  Kind of like Legion from the Marvel Comics.