On first appearance, these Links are more like your typical humans. However, these Links have four eyes. See the picture for what I am talking about. A simple baseball hat or bandana can cover the two upper eyes with ease so that they can blend in with humans. As a side effect, the two normal eyes cannot read text of any size, as they are far-sighted. The other two eyes are thus near-sighted. When all four eyes work in conjuncture with each other, they are more powerful than the sight in any living organism or Link. The total power of their sight is un-measurable by human or Special Unit 2 standards. If an analogy has to be made, the Quadregas has sight more powerful than a microscope or telescope. Special Unit 2 has been trying to convince one join up, but with power like that comes egos, greed, etc It is hardly worth it, considering how bad their attitudes are towards people with two eyes.
Little known fact: Based on a bet Stan was able to count the number of flecks of sand there were in a 32. oz. Glass. Carl at the time wasn't aware of the powers these Links had or what made them so special. Thus, Carl was forced to pay up and the animosity between them has grown through the years.
You can kill a Quadregas with standard ammo. They may see you a mile away, but they are not that bright. If a QD dons a hat or is, some how covering its odd eyes then you can take them out with no problem.