The Grim Adventures of Billy & Mandy is a show chock full of total gamegeek fodder and it happens to be one of the best cartoons to come along in years. I suppose you could even set the adventure at Toadblatt's Summer School of Sorcery, the Harry Potter takeoff in the show, to riff off the dueling academies in the Yu-Gi-Oh cartoon.
I think the whole concept could be made to work, but I don't really think I'm going to pursue it. I've really grown to like con games where I can hand out character sheets and we start playing immediately. The thought of going over the basic deal of Pokéthulhu and then going over the basic deal of Billy & Mandy and only then playing kinda fills me with dread. I'd much rather hand out utterly inexplicable Encounter Critical charsheets, announce "you're all playing mutant robot hookers exploring a dungeon underneath the Face on Mars" and then start slinging dice. Some games get me into that groove and others do not. (Ridiculously, I think running an entire Billy & Mandy-themed campaign of Pokéthulhu would be more fun than struggling with the learning curve of a one shot.)
I also like con games where characters are rolled up one the spot. That works great for games where you mostly throw some stat dice and look up silly charts. I've gone that route for my OD&D and Basic/Expert con games in recent years. For games with point buys, long skill lists, or heavy math formulae this method doesn't work so well.
Hmmm, I think this whole post could be summed up as "I like stupid games. No, no! Even stupider than that!" No big surprise there. Usually when I try to run something smart and sophisiticated it blows up in my face. But honestly and unabashedly dumb games work for me with much greater frequency.