C'thun and Yogg-Saron.
C'thun and Yogg-Saron.
The Old Gods are the most disturbing for me because they're beings of pure evil. They don't have any rationale behind what they're trying to do, they just want to murder everyone and everything. Lich King was pretty terrifying due to his past, but bosses like Kil'Jaeden and Deathwing I just have no real excitement when killing them. Oh, they want to kill us just like everyone else on this planet? Meh.
Yogg-Saron definately creeps me out, and his voice and speech are my favourites in game. "I am the lucid dream, the monster in your nightmares.." -beginning with Sara, best of them all, hands down!
Lich King had the best lore and most epic fight, but still Yoggsie is my number one.
http://www.youtube.com/watch?v=ZRLgx1sjwp0&t=2m45s
Or, go 2min 45 seconds in the embeded:
I am the lucid dream,
The monster in your nightmares,
The fiend of a thousand faces,
Cower before my true form,
Bow down before the God of death!
I am the lucid dream
Uulwi ifis halahs gag erh'ongg w'ssh