On Berk, everyone was riding their Dragons, doing business in the bushes and eating fish. That night, a wormhole appeared, and Fishlegs looked at it. Suddenly, a giant mass came out. It was 60 feet long, 30 feet tall and had a fin on its back. As Gobber the Blech started to look at it, the creature stepped on him, making him scream "Help!" in a muffled voice. Asrid was the only one who heard him, and she screamed like hell. "Hiccup! What is this?". Hiccup came to her and didn't know what it was, but he quickly called it a "Finned Nightmare". By then, Gobber was half eaten, and being scavenged by Bird like creatures with long tails, sharp teeth and no feathers. Fishlegs calls them "Tweety Vultures".
MiddleMany other creatures were coming from the wormhole. One of them had sickle shaped claws on its feet, and Stoick called them 'Sickled Braniacs". Three attacked Toothless, but he could kill them. Both Hiccup and Astrid got on their Dragons and went to solve this problem. They attacked the Sickled Braniacs and incinerated them, but then, a huge, 50 foot mass about 23 foot tall tossed the Finned Nightmare into the sky, and roared so lound it knocked all Dragons out of the air. It had huge jaws with sharp teeth, and all the other Dragon like creatures ran back where they came frrom. It ate Fishlegs, Ruffnut and killed Fireworm. A Gronkle managed to lick up and eat the Tweety Vultures, but was stepped on by another Finned Nightmare that combusts due to Terrible Terrors burning up its insides with their fire.
The Dragons got back into the air and conjfused it. It roared in rage. When it did so Astrid made her Deadly Nadder fire into its mouth, and Hiccup made Toothless spew fire into the flames. The creature blew up, and all was solved. Astrid and Hiccup both agreed to call it "Killer Nightmare".
But Was All Solved?
No. T.rex eggs hatched and made their way to Berk. But that's an SR or Manga Maniac fanon. :)