A can think of a couple examples, energy sword elites from halo. Oh also the flood, more out of irritation. Egregious amounts of out-of-sight rocket ninjas from ninja gaiden. But personally one enemy that I doubt will ever get topped(not bosses, just plain jane enemies) was the shadow cats from dmc1. If you've played it, you know why.
Edit: If you haven't, I should probably tell you why.
[img/]http://images.wikia.com/devilmaycry/images/1/15/Demonic_Shadow_Cat.jpg[/img]
They weren't scary, in fact this one looks kind of sad, but they were the toughest enemy in any "action" game that I've ever played. These things were so ridiculous that they removed the enemy entirely from "easy" mode. They had a rather difficult to dodge lunge attack, had an enormous health pool that could only be damaged by exposing their core and beating on it. Also in dmd mode when they dt'd you had to stay on the furthest side of the room until it was over. This enemy was an arsehole.
So, what enemies have been scarred into your memory?
Edit: If you haven't, I should probably tell you why.
[img/]http://images.wikia.com/devilmaycry/images/1/15/Demonic_Shadow_Cat.jpg[/img]
They weren't scary, in fact this one looks kind of sad, but they were the toughest enemy in any "action" game that I've ever played. These things were so ridiculous that they removed the enemy entirely from "easy" mode. They had a rather difficult to dodge lunge attack, had an enormous health pool that could only be damaged by exposing their core and beating on it. Also in dmd mode when they dt'd you had to stay on the furthest side of the room until it was over. This enemy was an arsehole.
So, what enemies have been scarred into your memory?