You could have guests dress up as their favorite comic strip characters. Decorate the place with old comic strips and have a comic-themed cake.
You could have characters dressed up as superheroes or princesses. Or maybe show a cake with candles that look like they're about to blow out.
You could have a superhero-themed party with everyone dressing up as their favorite comic heroes. Also, decorate the place with comic book covers and serve treats shaped like comic characters.
You could create a comic strip of the birthday person's favorite childhood memory. It'll be a unique and touching gift.
You could have a superhero-themed comic strip party. Decorate with comic book covers and have guests dress up as their favorite superheroes.
How about a collection of popular comic strips signed by the artists? That would be a special treat. Also, a DIY comic strip kit with all the supplies needed for the person to create their own could be fun.
You could have a theme based on the birthday person's favorite comic characters. Decorate with their posters and have custom cupcakes with the characters on top.
You could focus on the emotions of the participants, showing their determination and anger. Or maybe illustrate the chaos of the event with detailed scenes of tea being thrown into the water.
You could have guests dress up as their favorite caricature characters. Also, have a caricature artist draw guests' portraits as party favors.
You could have comic-themed balloons and banners. Also, get some cutouts of popular comic characters to stick on the walls.
Well, you could include a 'Capture the Flag' game like they have at Camp Half - Blood. It would be exciting for the characters in the fanfiction. Also, for the party decorations, having floating Greek columns made of cardboard and painted to look like marble would be really cool. And don't forget about a 'prophecy - writing' station where guests can create their own prophecies, just like in the books.