So I've got this character in my head for the Rogues Gallery, and I'm not sure how to define his super-power, which is, essentially, to perplex the hell out of the author.  How would you handle that as a WGP aspect?

Between the real world and the Fictionverse lies the chaotic, kaleidoscopic realm of the imagination, also known as the Land of Do-As-You-Please, or Fantasia.  Here the past is whatever you want it to be, and hurricane-force brainstorms thunder over the shifting landscape.  The Baffler is a terrifying figure of this place--a combination of a serial kiler, Big Bad Wolf, boogeyman, and the awful thing just behind you when you're alone in the dark.  He escaped from the inescapable Logic Prisons and drove five Class XII Reasoners incurably insane in the process.  As a terrorist of inexplicability (sometimes he is a warlord in control of an entire realm, sometimes not--who can say why?) he conducted raids on the Fictionverse for some time, until he broke into the real world.  Though the Baffler is frequently opposed by Paper Tiger and even Descripto the Super-Descibable Boy, he is most often thwarted by The Complicated Mr. Van der Waals. 

The Baffler derives power from the tornadoes of Uncertainty that rip across Fantasia, the backstage of the cosmos.  In fact he may even be the personification of such a storm.  In any event, he creates narrative incoherence wherever he goes.  His true target is aways the Author of the story (me, I guess) [ed. - this was a notebook, not originally intended as an RPG thing with collective authorship] and he draws power from the author's confusion.

One time the complicated Mr. Van der Waals defeated the Baffler by switching to a more stable narrative structure: instead of a superhero story where anyhting goes, things got switched into a Victorian novel like Jane Eyre, and this boring dull world rendered the Baffler powerless--though maybe the cure was worse than the disease!  This "switching narrative structures" trick lets you tell genre-bending stories that don't fit the usual comic book world.

Wow, James. You've been sleeping with the Phantom Tollbooth and Jasper Fforde under your pillow again, haven't you?

The key for making powers work in WGP... is just that everyone understands how to describe them, visually. What does it look like in the imaginary comic when the Baffler destroys narrative continuity? Does he tear pieces off the background to reveal badly-photocopied Jack Kirby pages and then grab the grainy Ultimate Nullifier to threaten the heroes? Does he shatter the panel borders themselves? Does he stare right off the page and break the 4th wall by gloating to the author? So long as all the players understand how this power is going to manifest, I think it will work fine.

Personally, I'd title the power "Manxome" but I've always loved Jabberwocky.