Xykon is basically an idiot. He clowns around a lot, while Harry is pretty much business.
Most importantly, he doesn't get buffing time - with buffing he can fly and do other good ****, but as-is he's a landbound caster who takes six seconds to cast against somebody who can do long-ranged grapples with divine fists of energy. You know, like a certain D&D spell designed to screw over casters.
Also, writeup of Dresden's stuff from an unbiased source: http://en.wikipedia.org/wiki/Harry_Dresden#Powers_and_abilities
'yeah'. He's a fair bit better than Xykon at the blasty thing, which is all Xykon is going to get because he's not going to take a dude that looks like he came out of World of Darkness seriously.
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Sburbopolis, Homestuck RPG: http://www.gamefaqs.com/boards/8-gamefaqs-contests/60981373