Hijack

With Jack being the only other male in the crossover, the two are usually portrayed to be good friends, though it can sometimes go beyond a platonic relationship. "Hijack" or "Frostcup", as most fans call it, originates to a time before RotBTD when Rise of the Guardians and How to Train Your Dragon ("How to Train Your Guardian") was a crossover on its own. Since Jack Frost (Jokuli Frost) comes from Nordic myths and Hiccup is a Viking, fans belief it could have been possible that Hiccup believed in Jack, and therefore been able to see him. Also, it is said that on Hiccup's native island of Berk it "snows nine months of the year and hails the other three". Though this could be a bit of an exaggeration, it is a fact that the island has some cold weather patterns, which could be a result of frequent visits from Jack.