Mine would have to be zant's hand from TP's. During hole game it was the only thing that scared the crap out of me because youre holding that stone and youre freakeing out you know it's right behind trying to get the stone back so youre rushing with the parts of the clawshot and you cant quiet hit that target and then you finaly calm youreself down and right before you press the B button for the target......BAM it hits you and in anger and fear I scream.
I have to go with the Iron Knuckles in OoT because they are always a challenge and then you have to beat the gigantic one that has Nabooru inside it. The Stalfos in any game is a challenge. I guess i like the harder enemies.