What kind of world ending catastrophe would it take for all of the characters to come together to fight? Greek, Roman, Norse, Egyptian, and all the Rick Riordan presents. Hero’s, gods, everyone. We’ve seen some of the characters crossing over for small parts and adventures but what would it take for all of them to meet. It couldn’t be the world ending because that’s been stopped so many times so what would it have to be. And how do you think all the characters would react and interact. Some already know about the other gods, but I have a feeling it would take a lot for everyone to join together.