The Bewilderbeast is a massive species of dragon, dwarfing nearly all other species. It has a stocky body with a large head. It's face is fairly flat, with two massive tusks and a crown of spikes. Numerous spikes also cover it's back and tail. It's wings have regressed into fin-like structures, and it can no longer fly. Several fins line it's tail and legs as well. So far bewilderbeasts have been seen to be nearly all white, or possess a more gray complexion.
Three of these dragons have been seen thus far; two alive and one dead. The deceased bewilderbeast was seen on Vanaheim; the island where most dragons go to die, where its skeleton made up part of the island's landscape. The second, which was alpha of all dragons in the region, was content to live within a nest of ice it created peacefully for many years where it met the viking woman Valka Haddock, wife of Stoick the Vast and the mother of Hiccup Haddock, the viking who would bond with Toothless, the night fury. The third was captured as an egg by Drago Bludvist and tortured into serving him. Eventually, Drago's bewilderbeast attacked the white alpha's home, provoking the dragon into a rage, and igniting a battle to the death between the two alpha dragons, with Drago's bewilderbeast impaling the former alpha after a short but intense battle. After conquering the dead alpha's dragons and enslaving Toothless, Drago then used his new alpha to try and attack the village of Berk and take its dragons under his control, though the actions of Hiccup and Toothless eventually repelled the bewilderbeast and broke one of its tusks, with Toothless asserting himself as the new alpha. The defeated bewilderbeast then retreated into the sea, with Drago still atop its back, leaving its fate unknown. It was later revealed that Drago's Bewilderbeast later escaped to the Hidden World, where it happily lived and submitted to Toothless as its king, indicating that it had forgiven him for their fight and bore him no ill will.
Bewilderbeasts appear to be mostly aquatic, and prefer to live in cold regions, where they make a dome of ice to shelter themselves, usually only leaving to hunt fish or defend their homes. As they are aquatic, they are classified as Class 10 leviathan dragons (the marine equivalent to Titan Wing dragons).
Wild bewilderbeasts appear to be remarkably gentle and tolerant dragons for the most part, taking no issue with humans and strange dragons entering their homes, and in the case of Valka's bewilderbeast, baby dragons playing on and around its face. Additionally, wild bewilderbeasts appear to have a mutualistic relationship with its subordinates, as the Alpha helps shelter and feed them, and in turn the subordinates help the alpha in its battles and to protect the nest. However, both of the seen bewilderbeasts took threats very seriously, and while they often called in underlings to help them, they were quick to join fights themselves. Drago's bewilderbeast was an exception to this, acting out of a desire to please the cruel master who instilled fear into it, and acting like a mistreated beast of burden.
When in battle, bewilderbeasts are slow, but make excellent use of their enormous bulk and massive tusks to crush or impale foes.
Unlike most dragons, bewilderbeasts do not breath fire, but rather spit freezing water that quickly solidifies into an aqua-colored ice, freezing enemies solid and destroying large structures easily.
Bewilderbeasts also can summon or forcibly control lesser dragons nearby to have them aid the creature in fights. They can telepathically control other, lesser dragons. This control can be broken however, and any dragon regardless of species that challenges the alpha bewilderbeast and wins will become the new alpha of the dragons under its care or control. This ability to control other dragons is a power they may share with the Red Death, but no one knows for certain.
Bewilderbeasts also appear to be resistant to cold, able to hold their breath for incredibly long periods, swim quite fast through water, and are quite resistant to damage from other dragons' fire, though a night fury's full powered shot was seen to break off a bewilderbeast's tusk.