A single game of Maces and Talons.

If Viggo wins, he gets Hiccup for a night. If Hiccup wins, he gets Viggo for a day.

It’s not that Hiccup wants to spend a whole day with Viggo-freakin’-Grimborn. What he wants is a chance to change the man’s mind about dragons and a day is more than enough time for him to pick away at Viggo. (Hiccup tried fighting for an end to the war if he won, but even he had to reluctantly admit that wasn’t equal to what Viggo was asking for).

They didn’t account for a tie.

So now they have to split the difference. Six hours of Hiccup trying to show Viggo how amazing dragons are, six hours of Viggo trying to get Hiccup in his bed.

By the end of the twelve hours, Viggo is surprised by the sudden compassion he has for the beasts his tribe captures and Hiccup is surprised by the how much he longs to return to Viggo’s side.