I really like Zhaitan, dragon of death and shadow, from Guild Wars 2. I played a lot of the game before I ever saw the dragon (its the main antagonist of the base game) and figured that it would be just a kinda generic looking dragon, maybe looking a bit deathly and/or skeletal like it's minions.
Then, woah...

It has other heads coming out of its mouth and other heads making up its body. It's basically stitched together from different dragons and when you actually get to fight it at the end, it is monstrous.
