The following is the classification of aliens or commonly called the extraterrestial beings which i gathered from different sources mostly from the book written by Patrick Huyghe titled The Field Guide to Extraterrestrials and a book by Chancellor Press The Worlds Greatest UFO and Alien Encounters.

Extraterrestrials can be classified into five types with subtypes based on latest encounters with these beings.

The following I believe is more simple classification of aliens, a very confusing subject matter with regards to extraterrestrial research.

ALIEN TYPE 1: GREYS. This type of aliens has several subtypes. They were referred to as “grays or greys” because they all tend to appear greyish in color although there were reports some of this type has brighter colors like orange.

GREY TYPE A: Alien researchers said this type most commonly referred to as the greys. Also known as Zeta Reticuli from the Zeta Reticulan star system (the Bernard star) neighboring the Orion area. They function in a mode that is apparently military in nature with a rigidly defined social structure that holds science and “conquering worlds” to be the prime movers.
Description: They are normally about 4.5 ft tall with large heads and black “wrap around” eyes. They have limited facial features, slit mouth and no nose to speak of. They have evolved beyond the need for reproductive systems or digestive systems and reproduce by cloning. Their genetics is partly based on insectoidal genetics.

GREY TYPE B: These are tall Greys from Orion Constellation.
Description: They usually stand about 7 to 8 ft. tall although there were reports that they are about 9 to 12 ft. with facial feature somewhat similar to grey type A with the exception of the large nose found on type B Greys. These Greys also have technologies that allow them to perform certain actions that appear “miraculous.” These Greys are less viscous toward humans than type A Greys but believed to be “hostile”.

GREY TYPE C: These beings are believed to be from a star system near the shoulder of Orion called Bellatrax.
Description: These are the shortest of the Greys and tend to be about 3.5 ft. tall. Their facial features are very similar to the Zeta Reticuli greys and are of the same “root race.”. They are just as hostile to humans as the Zetas.

ALIEN TYPE 2: ANIMALIANS
REPTILIANS: These are considered to be the master species of type A Greys mostly from Zeta Reticuli Star System. Their own planet is becoming unable to adequately support life and they need somewhere else to live.
Description: Their genetics akin to reptiles. These are considered to be highly advanced entities but viewed as being of a negative, hostile or dangerous disposition since they regard humans as a totally inferior race. They would perceive humans much the way we would perceive a herd of cattle. They are carnivorous in regard to humans.

HAIRY MAMALIANS: Research is still going on about its existence and their point of origin. They suddenly appear in many places in this planet but no one has ever fully documented its manifestations although there were compiled photographs and stories about them. Some believed these creatures are capable of manifesting in the physical thru teleportation but this idea is not conclusive at all. Others inclined to believe that these beings were trapped in this planet and survived for hundreds of years.
Description: These type of extraterrestrials are distinguished themselves from the humanoids by hair that covers the creatures’ entire body, or at least all that is visible of it. Sighted big-foot like creatures are of this kind. Others appeared to be animals with four legs, or they are entities with bat-like faces. Yetis are considered to be under this alien type.

AMPHIBIANS: It was believed that these creatures They appeared as frog-like or fish-like (dolphin) entities. The type name refers only to creatures’ smooth skin and has nothing to do, with matters aquatic.

INSECTOIDS: This class includes all insect-like beings with long spindly limbs and large multifaceted eyes. There are many variants under this class, those creatures with rounded wings, others might call it fairies, and those resembling a grasshopper or praying mantis.

AVIAN: These are simply creatures with birdlike wings. There are reports of sightings of this class, known among these sightings is the creature commonly known as mothman.

ALIEN TYPE 3: HUMAN TYPE ALIENS
HUMAN TYPE A: These are of a genetic base similar to humans of earth. They appear of “normal” height (5-6ft?) and tend to be fair-skinned with blonde hair. These entities have been abducted by the greys or are the offspring of abductees and have been trained by the greys as servants. These entities are totally subservient to the greys.

HUMAN TYPE B: These are aliens of similar genetics to earth humans and also, it seems, of the humans that serve the greys. These are from the Pleiades and are also of the blonde, fair-skinned appearance. This type is of a genuine highly evolved, spiritual, benevolent variety and have a kinship toward humans and are the only aliens to be truly trusted by earth humans at this time. They had at one time offered to be of assistance to earth leaders in dealing with the alien situation here but were rebuffed and so have taken a kind of “hands off” approach for the time being. These aliens are supposedly the forefather race of humankind. These are apparently not on earth much at this time due to serious problems in the area of their home.

HUMAN TYPE C: Very little is known about these. They are supposedly another of the highly evolved, spiritual type of great benevolence to earth humans. I understand that their appearance is similar to other human-type aliens. They are from Sirius and don’t appear to be much involved with earth happenings at this time other than being concerned about the Grey scenario. They could desire to be of help to humans.
There are other known human type aliens of this “more highly spiritually evolved” nature that are apparently aware of the situation on earth and considering some possible course of action. These are from Arcturus and Vega.

ALIEN TYPE 4: ROBOTIC
Robotic aliens vary in height and appearance. Some are metallic with human-like shape others are plain metals and square shapes. They were seen at a height from 1.5 feet to 20 feet. UFO researcher Patrick Huyghe believed there are two types of extraterrestrials under this class.

METALLIC TYPE: These aliens appeared to be robots that look like cans or slabs of metal. Some believe that robotics under this type are results of extraterrestrial engineering projects. They were made to make experimental landings on prospective planets like Earth. Others are inclined to believe that these are another species of extraterrestrial life.

FLESHY TYPE: These are android-like beings that display features of living beings either human or animal. They also appear as robots with either humanlike arms or legs, for instance.

ALIEN TYPE 5: EXOTIC
The exotic type of aliens, according to Huyghe, are those don’t fall to any of the alien types earlier mentioned. These beings has unusual forms, shapes and manifestations. Alien investigators/researchers also call these beings as “sasquatch” because of their unique description uncomparable to another alien species. They are classified into two type.

PHYSICAL: Huyghe considered this type as catchall category and includes such variants as an entity in the shape of a brain and a blob-like thing. Other unusual creatures such as chupacabra in Puerto Rico can fall under this category.

APPARITIONAL: These are ghostlike entities and non-humanoid creatures that are partially formed and look as if they exist at least in part in another dimension. Although I believe extraterrestrials per se are non-physical entities, beings under this category can’t manifest in the physical form and shapes. They can be seen as transparent entities, a light and others.