Ascended Fanon: Of a sort. A popular fan-created mock cover for The Blood of Olympus was licensed by Disney to appear as a poster in the Wal-Mart exclusive edition of the book.
Fan Nickname: Camp Purple/Camp Bizarro/Camp More-Badass-Than-Thou for the Roman demigod camp, Camp Jupiter.
I Knew It!: Acclaimed fanartist Viria drew this picture four months before House of Hades with Calypso's reappearance and romance with Leo was released.
Before Son of Neptune, many viewers speculated who the other four of the seven were. Annabeth was correctly guessed - but Reyna was another common guess as well. In a bizarre way, Reyna turned out to be one of the most important characters in the series and gets to be a viewpoint character in the final book.
Trolling Creator: Riordan dedicated the fourth book House of Hades, to the readers. It says "To my wonderful readers: Sorry about that last cliff-hanger. Well, no, not really. HAHAHAHA. But seriously, I love you guys."
He apologizes for this in the dedication for the fifth book, but says "I'll try to avoid cliffhangers in this book. Well, except for maybe a few small ones... because I love you guys."