This is a idea that I had. What if Viggo had survived falling into a volcano in a different method. In my opinion he is too smart not have had an escape plan for after he got the Dragon Eye back in the end of Shell Shocked Part 2.
Escaping from the cell on the Defenders of the Wing island had been laughably easy. Once the attack had started, no one had kept watch on him, so he had simply opened the cell door, which was broken after one of Shellfire attacks had hit it.
"Once I retrieve the Dragon Eye, you will ensure I get out safely?" confirmed Viggo, tossing the sack of gold to Krogan. They were mere miles from the Edge, planning on how the next day would go.
"Just makes sure you don't lose the Dragon Eye," Krogan said, reminding Viggo that Krogan had other motivations to agree, rather than just the money. "Why go through all these hardships, when you already have the Dragon Eye, and the means to defeat Ryker?"
"I find it amusing to let the enemy think they have the upper hand, just to realize they have been playing right into my hand the entire time. I wouldn't expect you to understand."
"Don't you have a meeting with your little dragon rider friends?" asked Krogan, changing the subject.
Getting onto the Edge was not hard, as none of the Dragon Riders would expect a "trained" Monstrous Nightmare to be carrying their enemy. He dismissed Krogan to stay in the forest, while he searched for Hiccup. Hearing a familiar voice, he walked towards it, and hearing the uncertainty in the voice, he thought This will be only too easy.