This is the robot guard. Basically, it moves back and forth until it spots the player, then it starts shooting. You can actually see in the screenshot that I shot at a robot guard at the same time the robot guard shot back, and the bullets cross each other.
There is, however, still a major bug with this enemy. When the robot is looking to the right it almost never spots the player, however when looking to the left it always spots the player. I can not pinpoint the cause of this, and I must have looked over the code for this enemy 3 times looking for the source of the bug. I'm still testing it though, so I'll probably find it.
One last note about it. Over to the left on this screenshot you can see one of the robot's remains that I've killed. When a robot is shot, it plays a death animation(where it explodes), but the remains of the robot stay on the ground. I thought that was a nice touch, as opposed to the robot just dissapearing.