User blog:Megadracosaurus/Cross-overs

Me and a friend spoke a few days about cross-overs, after seeing 'Heroes United', a Crossover between Ben 10 and Generator Rex. Seeing how we are both HTTYD-Fans, we talked about the possibility of a HTTYD-Crossover. However, we couldn't think of another franchise that fits in the HTTYD-World, or was serious enough. Does Anyone has any ideas? If DreamWorks would decide to make a Crossover with HTTYD, what Other franchise should it be?