I love dragons and can list a lot of my favorites, top being Princess Flame from Drazing Blagons, but not all dragons are likeable to me, even as a villain.
So, who is my least favorite dragon?
One from a unique fantasy world with some amazing songs, lovable characters, there was a big battle that changed the world and resulted in many deaths, later revealed to be caused by a hidden immortal godlike antagonist who feels superior to everyone else, and in the present day, the main character lost their parents at a young age but discovers a mystical power and leaves their hometown with a comical sidekick, meeting new friends along the way, and three big races (one of which has wings) come together, inspired by the main characters (including a princess of the race with wings).
Then, this dragon comes in, this universe's definitive Spike, but far worse, and nearly ruins the whole experience. Anyone who knows him hates him with a passion, myself included!
Yes, I am talking about...
Dragon King Alcar from Xenoblade Chronicles!
Even if you are overleveled, his Spike damage can kill you pretty easily. The only way to stop him (aside from reducing spike damage with Spike Defence gems, if you were able to get any) is to have Shulk use Purge, but that doesn't always hit, and if it misses, you have to attack him (thus taking the Spike damage) to replenish your Monado meter (that or sacrifice half your HP to do so), and keep using Purge until it blocks his Spike.
That, or get a Chain Attack ready early in and topple him, his Spike is ineffective when toppled I think.