The Night Fury is the rarest and most intelligent species of dragon. Night Furies are generally quite aggressive to any form of threat they find. According to the Dragon Manual, the Night Fury is considered to be so aggressive that it is likened to the "unholy offspring of lightning and Death itself." Also like it's fellow dragons, Night Furies are seen to have a different personality when they are not threatened. They are curious creatures that attempt to understand new things they observe and are intelligent enough to recreate the actions that they see.I'd say that sounds a lot like Bear.
In the movie, Toothless takes Hiccup on wild rides, spins him around, threatens to eat him, wakes him up by jumping on him in bed, bounces on the furniture, teaches him about himself, takes him places he'd never thought he'd go, scares the hell out of him, challenges him at every move...and makes him smile. See, he's a Night Fury!
They manage to tame their dragons, right?