For me it was Kai Leng in Mass Effect 3. In the intro cinematic he looked like a cool assassin that was sent after Shepard, but when you meet him he’s just a loser dweeb with insane plot armor and the power of anime on his side.

Another character for me is Alduin in Skyrim. The entire storyline hyped him up as The World Eater, that he will bring the apocalypse, but the when you do finally face him… I stg I’ve fought Draugr more fearsome.