Mammal/Hybrid-based creatures

Zombies

A zombie researcher, seen during the Mansion incident.
A zombie (in the Resident Evil series) refers to any person that has succumbed to the T-Virus and has been turned into a reanimated corpse that feeds on human flesh. The incubation period for the virus varies depending on the circumstances. A human will eventually turn into a zombie some time after the initial exposure to the virus, this can be a week in some cases though it is generally within a few hours, sometimes even minutes. This is usually after being heavily injured or killed by a T- Virus carrier. The most notable symptom prior to mutation is the itchiness that results from the carrier's increased metabolism.
A zombie has lost any sense of reasoning and is driven completely by instincts. A zombie will pursue its prey, until it has lost enough blood or through decapitation or complete destruction of the head. A zombie can resist several gunshots from a typical 9mm handgun before falling down, but can be easily killed with either: a well-aimed shotgun blast to the head or a high-caliber magnum handgun. However, there are also rare hyper zombies (not to be confused with "Crimson Heads") that will approach its prey very fast and are resistant to shotgun blasts. A zombie will continue to pursue its prey even after losing its limbs or lower half of the body. Zombies that have lost the use of their legs (either through deterioration or a well-aimed gunshot) will instead crawl towards its prey until they can bite their prey's leg. They can easily be stopped with one good stomp or kick to their head. Other zombies will lay dormant on the ground due to their lack of nutrition, but will bite anything that comes to their direction. Some zombies will pretend to be dead on the ground, only to rise up after a determined period has passed. The only way to determine a zombie's death is by checking whether there's a pool of blood under their body.
Since virtually anyone can become a zombie, they can come in different varieties depending on the location where an outbreak occurs. This ranges from ordinary civilians and police officers to workers and researchers that were experimenting on the virus. Some zombies were even created within Umbrella's facilities as a result of experiments and are usually completely naked. Individuals that have turned into zombies includes Edward Dewey (of S.T.A.R.S. Bravo Team), Forest Speyer (also of S.T.A.R.S.), Marvin Branagh, Murphy Seeker and Brad Vickers among others. Capabilities of a Zombie vary as factors dependent on the carrier. A zombie can also mutate into a Licker or a Crimson Head after prolonged exposure, depending on the circumstances and chance, as only very few zombies are actually resilient enough to evolve into a Licker or Evolved Licker naturally; most of these are the result of artificial gene manipulation.

Crimson Head

A recently ressurected Crimson Head
A Crimson Head (or V-Act) is a type of zombie. After the T-Virus infects a normal human being, it rapidly initiates a brain cell decline, but should the new zombie be knocked out. After a time, the zombies cell tissue regenerates and is more fresh, making it able to run. The T-Virus gives a little more intelligence to the monster, causing deeper necrotizing effects and terrible blood seeping, giving it a crimson skin, small claws, heavy resistance to common firearms, and a more aggressive attitude. Capable of a crouching sprint, clawing attacks, and limited jumping, a Crimson Head presents a significant threat to all but a heavily armed combatant. Essentially rendering sidearms useless, engagement with anything but an explosive or shotgun is highly discouraged. The process is only halted by immolating (burning) the fallen zombie, decapitation (entirely removing the head) or by blowing out its knee caps, thereby destroying any possibilty for regeneration and mutation. Areas in which a zombie was dispatched and left untended are to be deemed extremely hazardous, and any encounter with a Crimson Head where the combatant does not have access to more powerful weapons (I.E. Grenade Launchers, grenades, assault rifles) are under advisement to flee immediately. If the Crimson Head is killed, it will no longer resurrect itself.
Appears in: Resident Evil (remake)

Licker

One of the "Lickers" seen in the Raccoon Police Department.
A Licker is an irregular creature that is created when a zombie undergoes further mutation from a second exposure to the T-Virus. The creature got its name from its most distinguishing characteristic, its long sharp tongue which it uses to attack its prey. It also has its brain and muscle tissue exposed, as well as sharp claws on both of its arms. However, they don't have eyes and have to relied on their acute sense of hearing.
A Licker walks on four legs and can climb walls. It also has the ability to jump towards its prey at great heights. However, since a Licker relies on its hearing to track down its prey, its easily vulnerable to weapons that make little sound.
In addition to the regular Lickers, there were also Enhanced Licker located in Umbrella's Underground Research Facility in Raccoon City. These had a greater resistance and attack power than the regular Lickers.
Appears in: Resident Evil 2, Resident Evil Survivor, Resident Evil Survivor 2, Resident Evil Outbreak

Eliminator

Eliminators are bio-weapons created by James Marcus by implanting the T-Virus into a primate. They were one of the earliest bio-weapons created from Marcus' experiments, along with the Lurker and Plague Crawler. The mutation caused their muscle to rip through their skin giving them more strength and speed. They are very aggressive and viciously attack prey.
The Eliminators were considered successful experiments, but were not mass-produced since they only had enough intelligence to follow simple orders. Instead, Marcus saw the potential of mammals as viral carriers and decided to continue his experiments using human specimens.
Appears in: Resident Evil 0

Cerberus/Zombie Dog

 A Cerberus or Zombie Dog is a Dobermann that has turned into a bloodthirsty hell-hound as a result of the T-Virus and now attacks any living thing that comes into their proximity. They're faster and more aggressive than a regular human zombie. These dogs have parts of their internal organs and rib cage partially exposed. Although, the terms Cerberus and Zombie Dog are usually used almost interchangeably, there's a huge difference between a Cerberus and the average Zombie Dog.
A Cerberus was used as a test subject by Umbrella to test the effects on the T-Virus. They were given the code number of MA-39 and were named Cerberus after the mythological three-headed guardian of Hades. The Cerberuses were seen in the Arklay Research Facility (in Resident Evil) and running amok in the Arklay forest area (this pack was the one that killed Edward Dewey and Kevin Dooley, as well as Joseph Frost). Of these, most present some internal weakness, which points to a weakness in their viral strain. A few Cerberuses were also being transported within the Ecliptic Express (in Resident Evil 0) inside the train's Freight Car.

A Zombie Dog on the other hand, was created through accidental exposure to the T-Virus as a result of a viral outbreak. The Zombie Dogs seen in Raccoon City (in Resident Evil 2 and Resident Evil 3: Nemesis) were police dogs that ate contaminated dog food and became zombies. The Zombie Dogs in Rockfort Island Military Training Facility (in Resident Evil Code: Veronica) were military dogs used by Umbrella's Special Forces. Still, of these, most only experience slight skin necrotising effects, rendering their muscles in a near-perfect state. Aggression level is also increased, making them exceedingly dangerous. 

 Infected Bat/Bat

The Infected Bat is a large-sized T-Virus infected vampire bat seen inside the cathedral in Umbrella's Management Training Facility. It goes after its prey by calling out the assistance of other regular sized infected bats. There were also infected bats in Rockfort Island during the viral outbreak, but these showed no sign of size increase and could be easily deterred by fire.

Chimera

A Chimera (which received its name from the mythical Greek creature) is a B.O.W. that was created by inserting fly DNA and the T-Virus into human specimens. They were being manufactured inside the Arklay Research Facility's basement lab and made that section of the facility (particularly the Power Generator room) into their habitat during the Mansion incident. Aside from their fly-like appearance, the Chimera's most notable characteristics is their ability to walk over walls and ceilings. They usually use the air ducts to travel from one part of the lab to the other and attack with their claw-like limbs.

Lisa is a hideously deformed human, a by-product of the Nemesis parasite injection, with what looks like a large yellow eye on her back, wears tattered clothing, a wooden manacle, fetters and a mask made of several human faces. She can be heard wandering around the Spencer Mansion, dragging her shackles and screaming cries of agony. During the mansion incident (the events of the game), she encounters and attacks the members of S.T.A.R.S. Alpha Team during their investigation of the residence. She is seemingly impervious to their firepower and attacks with tentacles that come out from her body.

Hunter

Hunters are bipedal reptilian-like creatures with large claws and teeth, and are noted for their loud shriek. They are actually B.O.Ws (Bio Organic Weapons) designed by the Umbrella Corporation by combining a fertilized human ovum with reptilian DNA and then implanting the T-Virus into the resulting creature.

Types of Hunters

MA-121 Hunter Alpha

Hunter model featured in "Resident Evil 0" and "Resident Evil", as well as in "Resident Evil: Survivor". The first successful Hunter model, the Alpha model was developed by Albert Wesker and William Birkin within the Arklay Research Facility in the Arklay Mountains. During the T-Virus outbreak in Raccoon Forest, the Hunters were released by the ressurrected James Marcus to eliminate Rebecca Chambers and Billy Coen when they were in the facility. Due to their large numbers, they eventually escaped the manor and later found their way into the Arklay Mansion, where they went after the surviving members of S.T.A.R.S.

Sometimes encountered in the Resident Evil Code Veronica, these creatures are identical in every way to Alphas except their purple skin, increased resistance, and their poisonous attack.

MA-121 Hunter Beta

 A variation of the standard Hunter (featured in Resident Evil 3: Nemesis) based on battle data collected from the Alpha model in the Arklay mansion. These were being transported to Raccoon City, via truck, in order to obtain their final combat data before they were mass-produced. With the viral outbreak taking over town, the truck never left Raccoon City, and eventually the Hunters escaped to several city areas. One of the most notable aspects of the Beta model were their large left arm, making them left-handed. Though they are significantly quicker than the Alpha model and had an improved nervous system that helped them to evade bullets, they lack the same fighting prowess.

 Anamphibian version of the Hunter (featured in Resident Evil 3: Nemesis and Resident Evil Outbreak). Nicknamed Frogger/Blocker due to its frog-like appearance. The Gamma model has no eyes or teeth. Instead, it has a large mouth that allows it to swallow its prey whole. They were secretly being harvested in tubes within a small lab in the Raccoon General Hospital, and make their home in the watery areas of the basement of the hospital. Due to their amphibious nature, they are exceedingly difficult to transport and mantain. Therefore, the only existing Gamma models were experimental ones, as they were not mass-produced.

MA-125 Hunter R

 A faster variation of the Alpha model (appearing in Resident Evil Outbreak). Similar to the Alpha mode in terms of appearances. Some of its distinguishing characteristics includes smaller claws and spikes on its back. It is thought that this Hunter variation was developed under the orders of William Birkin himself, and that the mutations come from increasing the amount of human material in their systems. Though, it is dubious this model will ever be mass-produced, as the test combat data on it was not recorded and all related data was consumed in the laboratories of William Birkin.

Enhanced Hunter

Hunter model featured in Resident Evil Code: Veronica. Also known as the Hunter II model. This model was not developed by Umbrella, but by Albert Wesker's mysterious employer after leaving Umbrella. This model was more intelligent than any of Umbrella's models, as it could track down its target through an automated surveillance device called a Seeker, which directed the Hunter directly against the target received by the device with a special frequency.

A variation of the Enhanced Hunter, the Sweeper has purple, reptilian scales, as well as venomous claws to distinguish it from the regular Enhanced model.

Hunter Elite

Hunter model appearing in Resident Evil: Dead Aim . The Hunter Elite is said to be faster and more powerful than the standard Hunter. As well, they are far more agile and powerful, requiring larger amounts of ammunition to be taken out due to their more resilient nature. Against it, they lacked the Hunter's common claws, forcing them to use their bare hands as combat weapons.

Tyrant

A Tyrant is a recurring breed of fictional creatures in the Resident Evil series. It is the Umbrella Corporation's ultimate Bio-Organic Weapon (B.O.W), designed to be the perfect soldier in any battle situation. Designed through surgical alterations and direct exposure to a large amount of the T-Virus administered to a living host, the Tyrant possesses superior strength and some even have super-human speed. The 'T' in T-Virus in fact stands for "Tyrant", because the ultimate creation of the virus is the Tyrant. This is why Tyrants have figured largely as final, or near-final bosses in most Resident Evil titles. Most humans, when exposed to the T-Virus, become zombies. About one in 10 million can assimilate the virus and become Tyrants. The process is more likely to occur during puberty because of a certain hormone, known as Beta Hetero Nonserotonin, created by a child's brain when under stress. It is for this reason that the hormone is extracted when the subject is conscious without anaesthetic to maximize stress levels and thus hormone production.

Main Types of Tyrants

Proto-Tyrant

The Proto-Tyrant was the predecessor to the T-002 Tyrant. Standing over 250cm tall, the Proto-Tyrant could deliver enormously powerful attacks with its huge body and claw-like digits, easily delivering instant death to anything it targeted.

Although it resembled the finished Tyrant model greatly, it was mentally unstable and lacked higher reasoning. Moreover, the Proto-Tyrant's body decayed significantly due to an overabundance of the T-Virus. As a result, the Proto-Tyrant couldn't be used effectively as a B.O.W. and was scheduled to be destroyed.

However, the Proto-Tyrant was released from its containment within Umbrella's Underground Lab in Raccoon City when S.T.A.R.S. operative Rebecca Chambers was in the area (in Resident Evil 0). The Tyrant's fatal flaw was the fact that its mutations had exposed its spinal column, providing a vulnerable target for Rebecca; the creature may not have been susceptible to conventional weaponry otherwise. Although Rebecca thwarted the Proto-Tyrant temporarily, it soon managed to recover and followed Rebecca into the underground Treatment Plant after reconvening with Billy Coen. With their combined firepower, Billy and Rebecca put a permanent end to the Proto-Tyrant.

T-002 Tyrant

.The T-002 Tyrant was the first truly completed Tyrant model (appearing in the original Resident Evil). Developed within Umbrella's secret Arklay Laboratory under the Spencer Mansion, improvements over the Proto-Tyrant include virtual invulnerability to small arms and better reasoning abilities, along with longer talons. Although the T-002 model appeared wild, in reality it could obey orders quite well

During the mansion incident, Wesker released the Tyrant from its containment and ordered it to attack Jill and Chris only to be impaled upon the claws of its talons; Wesker, however, had figured this into his plot to betray Umbrella, and once he would be resurrected by his mysterious virus, he would then take the Tyrant and jump ship to a rival company. The STARS members, however, subdued the beast, but when they attempted to make their escape from the mansion, the Tyrant returned, rejuvenated and now fully prepared for battle after undergoing its limit release phase, which was made evident by the reddish hue its integument took on. The beast was now superhumanly agile, but it was eventually destroyed by a rocket launcher dropped by Brad Vickers.

It also appears in Marvel vs. Capcom 2, Jill Valentine (who could summon zombies as a fighting tactic which is very ironic) can also summon him in a super move. If the opponent comes in contact, this guy appears and does a big job. He's a lot bigger than usual as well.

T-103 Tyrant

Colloquially known as Mr. X, the Mass-Produced T-103 Tyrant first appeared in Resident Evil 2 and has also made appearances in Resident Evil: Survivor, Resident Evil Outbreak File #2 and even a brief cameo near the ending of Resident Evil 3: Nemesis. It is the only Tyrant model ever to be mass-produced by Umbrella. These Tyrants were produced at Sheena Island by infusing hosts with Beta Hetero Nonserotonin extracted from children; without this treatment, only one in ten million normal humans would accept the T-Virus and become a Tyrant. The T-103 has a far more human-like appearance than the other Tyrant models, although it still stands out due to its inability to speak and its great height. The T-103 can recover from injuries faster than the T-002 due to high metabolism and extremely efficient cellular self-repairs. Furthermore, the T-103 is equipped with a "limiter" inside its defense coat, which is used to force it to follow orders.

Umbrella deployed one of their T-103 units via helicopter into the RPD Precinct in order to retrieve the G-Virus from the Birkins, as well as to dispose of Leon and Claire before they could find out the truth. The Tyrant had several encounters with one of them, as well as Umbrella agent HUNK, before falling into molten metal. After removing its Limiter, this Tyrant transformed into a Super Tyrant, with an appearance closer to that of previous models, including talon-like digits upon both of its hands as well as great speed and agility. Either Leon or Claire eventually managed to defeat it with the rocket launcher dropped by Ada Wong.

The rest of the T-103 units that were transported via helicopter were dropped to the Waste Factory located behind Raccoon Park to eliminate the U.S. Army unit that was sent by the Government to retrieve William Birkin and the G-Virus. The soldiers were acting based on falsified intelligence given to them by an Umbrella spy and led to a trap. The Tyrants were destroyed, but not before taking the entire Army squad as casualties with them. Jill finds the remains of the soldiers and one of the Tyrants near the Paracelcus' Sword rail cannon while exploring the Waste Factory.

T-103

An experimental T-103 variant, designation T-0400TP, was located within the Raccoon City Umbrella laboratory. This experimental model is faster and stronger than the original T-103 units and also lacks the exposed heart once its limiter is removed. Once the outbreak began, and with the large number of Hunters roaming about, Umbrella scientists Linda and Carter felt it best to unleash the Tyrant to even the odds. Programming the creature with an MO Disk to eliminate all Hunters on the premises whilst not attacking any humans, the Tyrant seemed to follow orders well until it suddenly went berserk, killing Carter and knocking Linda unconscious. The creature would then go on to stalk the survivors of the Raccoon City outbreak located within the labs until it was defeated, prior to their escape from the subterranean laboratories. Making its way onto the streets of Raccoon City and removing its limiter, however, the Tyrant then transformed into the Tyrant-R, or a Super Tyrant. The creature again had to be defeated on the streets of the destroyed city before the survivors could attempt to make an escape; shortly after its defeat, however, the accidentally unleashed Nyx (a Biological Organic Weapon) captured and absorbed it.

Nemesis T-Type

The Nemesis model is a T-103 type that has been implanted with a new breed of parasitic organism known as NE-a. Despite this, it has enough differences between the standard T-103 model to be considered a different creature from the regular T-103 (and other Tyrants for that matter).

T-078 Tyrant

The Tyrant model deployed in Umbrella's Military Training Facility located in Rockfort Island for special forces training. It has no official model number, but it's often known as the T-078 (based on the label that appears over its capsule).

This model is actually a variation of the T-103 model, having its limiter removed and its claw-studded hands changed into club-like fists, but otherwise it is similar to a standard T-103 and has roughly the same attack power. Unlike many other Tyrants, this model did not possess a weak spot of any kind (for example, an exposed heart).

During the viral outbreak in Rockfort Island (the events of Resident Evil Code: Veronica), Alfred Ashford released this Tyrant from its capsule when Claire Redfield and Steve Burnside attempted to escape the island prison. During the initial confrontation, Claire encountered the Tyrant at the passageway to the Ashford's Palace and managed to easily defeat it. However, the Tyrant recovered and stalked her into the cargo plane they were using to escape. In this second encounter, the Tyrant now possessed exponential speed and agility, coupled with its great strength. Claire managed to defeat the beast eventually by ejecting a cargo box full of high-power explosives out of the plane with the Tyrant in tow, which blasted in midair, high above the ocean.

Other Types of Tyrants

Thanatos Tyrant

The second of the three Tyrants was Thanatos who was released by Greg Muller, a renegade employee of Umbrella who was against mass-production of the Tyrants. The events in Resident Evil Outbreak showed just how powerful and agile the monster was; in fact, it successfully destroyed an entire U.B.C.S. unit effortlessly. Thanatos would then go on to attack the remaining survivors of the city-wide outbreak, who had came to the University to unearth answers, but the creature was temporarily rendered unconscious by a blast of electricity enabling the survivors to accomplish what the UBCS squadron could not; during the prior attack upon Thanatos, the UBCS were instructed to obtain Thanatos' blood for use in the production of the Daylight, but needless to say, they failed. An amazing show of Thanatos' endurance and survival instinct came when Nicholai Ginovaef set demolition charges in Raccoon University, which exploded while Thanatos was still inside. It apparently survived the blast, unprecedented by its predecessors, with the resulting damage costing it one arm, so to compensate, the remaining left limb of the Tyrant, now known as Thanatos-R to signify its "rebirth", elongated to enormous proportions. Also, Thanatos-R now had the ability of jumping hundreds of feet into the air prior to crashing down upon its intended target which made it a formidable boss, but the creature was felled by the blast of a rocket launcher. Demonstrating its superiority over previous models, however, Thanatos-R returned for a third battle before ultimately being subdued by an ampoule filled with a sample of the Daylight, a cure to the T-Virus which acted by arresting all proliferation of the pathogen within cells thus making it lethal to any and all T-Virus infected Biological Organic Weapons. While the Thanatos lacked the capability of mass-production, most of the data collected on it helped create other BOWs such as the Bandersnatch in Resident Evil Code: Veronica.

The Hypnos Tyrant was seen in Sheena Island (in Resident Evil: Survivor), an experimental prototype that was created by implanting the Hypnos gene into a standard Tyrant model. The Hypnos gene was created by Dr. Klein (Lott and Lily's father) by implanting several cells into one organism and then eliminating the weaker cells through natural selection.

In its initial phase when protagonist Ark Thompson first encounters the Tyrant, it appears as a genderless, hairless youth posessing claws for digits in its preservation tank. Once it awakens, the Hypnos Tyrant proceeds to kill either the Umbrella commander of Sheena Island, Vincent Goldman; the sewer janitor, Andy Holland; or the UT Commander, depending upon the scenario paths selected. The creature, however, sustains sufficient damage from its battle in the hallway with Ark, thus transforming into its more aggressive second form, which includes massive talons upon its left hand and an enlarged mandible. After further damage, the Hypnos Tyrant then transformed into its final form which seems to be more of a regression than an evolution; in essence, becomes a hunched, primate-like being with an elongated tongue and razor-sharp talon, losing much of its former intelligence during the mutation. Also, the beast suffers from hypertonia, thus its muscles are excessively large, rendering it vulnerable to gunfire. The Hypnos Tyrant was eventually destroyed when it leapt upon Ark's escape helicopter just before the factory exploded, at which point a missile was propelled into its abdomen, pushing it into the distance, and a second was launched to blow the Hypnos Tyrant away with the power of both detonated missiles. It's 3rd and final form looks a lot like Venom (comics), a villain from the Spider-Man series

T-091 Tyrant

Possessing tentacle-like digits on its hands, this Tyrant was fought by Bruce McGivern of Resident Evil: Dead Aim on the Spencer Rain just moments before its sinking. Thanks to its tentacle-like fingers, as mentioned earlier, it has the ability of striking from quite a distance away, but what it lacks is speed. Furthermore, the creature possesses an exposed tumor upon the posterior of its cervical region which proves detrimental to it in battle. Utilizing this weakness, Bruce blasts the tumor until the creature was no more.

Also known as the Reagent 092, the T-092 is effectively what Morpheus D. Duvall becomes once he injects himself with the TG-Virus. In effect, the T and G Viruses have been amalgamated on a molecular level thus this new virus allows its host to utilize electromagnetism in a variety of ways, including the generation of bolts of electricity and, most importantly, the ability to create an electromagnetic force field. Thanks to that said barrier, conventional weapons and attacks are rendered useless against the T-092 hence the creation of the Charged Particle Rifle. Apparently, the subject undergoes a sex change, as noted with Morpheus D. Duvall, and has awesome agility and power, but the T-092 can be defeated with the sheer power of the Charged Particle Rifle as it can tear through the creature's electromagnetic barrier. After sustaining enough damage, however, the uncontrollable transformation effects of the G-Virus take effect, transforming the T-092 into a blob-like being with a head capable of moving all about the large mass provided that it is its only weak point. Bruce, however, manages to blast the head of the beast enough times to destroy it.

Nemesis,

Nemesis is one of the deadliest bio organic weapons (B.O.W) created by Umbrella Corporation. His character model was based off a rejected design for Mr. X, a Tyrant featuring in Resident Evil 2. He is an 8 foot tall monster, wearing a black trenchcoat and boots. Other attributes include a deeply scarred, misshapen face, with tentacles hideously protruding from his upper-body. His left arm is smaller and less muscular compared to his right because of the numerous tentacles inside it.

William Birkin G-mutant

This creature was created when William Birkin injected himself with the unstable G-virus. The first form retains William's human-like form but has an enlarged right arm with an eye on his shoulder. The second form is still humanoid in appearance, though its right arm has giant claws and has a more fully developed eye on its shoulder; the carrier's original head is now part of its chest. The third form has four arms, two giant clawed arms formed from the carrier's original arms, and two smaller clawed arms. The fourth form has dropped down on all fours and its lower jaw has merged with its chest, lining it with rows of large teeth. Below the mouth it has two clawed arms. The fifth and final form doesn't really have a discernible shape; it looks like a giant pile of flesh, limbs, tentacles and eyes. Multiple organs have sprouted from the fleshy mass. It has a giant toothy mouth with all of the teeth pointing inwards. Further information: William Birkin

Bandersnatch
A Bandersnatch seen in the Rockfort Island Military Training Facility. A Bandersnatch is a type experimental bio-weapon that was designed within the Rockfort Island military training facility. The creature got its name from a similar being of the same name. The Bandersnatches were designed to be Tyrant-class bio-weapons with greater adaptability. It has an elongated right arm which it uses to grab and attack its prey or jump from one point to another. However, it lacks its left arm and has a devolved lower body.
Appears in: Resident Evil Code: Veronica, Resident Evil Survivor 2

Nosferatu

Nosferatu is named after the film by F.W. Murnau, who wanted to create a Dracula based movie but was unable to obtain the rights to the story. The result was "Nosferatu, eine Symphonie des Grauens" (A Symphony in horrors in German).
Nosferatu is the father of Alexia Ashford and Alfred Ashford, Alexander Ashford, who has been used in an experiment with the T-veronica virus by his own children, Alfred and Alexia. Alfred and Alexia considered Alexander a failure to the legacy of the Ashford family(one of the three founding families of Umbrella), and they showed no remorse at all in using their father as a test subject for Alexia's T-Veronica virus.
Alexander, due to the T-Veronica virus, had mutated to the creature known as Nosferatu. His skin has discolored into a greenish gray and has a black blood soaked blindfold over his eyes, which may have been surgically removed or may have deteriorated due to the mutation. His clothes consist of army boots and apparently a skirt made of a heavy material(perhaps canvas). His hands are shakled to the back of his body as a result of his forced inprisonment. His main mutations are his majour tendrils sprouting from his back and his ability to produce toxic gas clouds(perhas owing to Alexia's experimentation with ant DNA to create the T-Veronica virus). Like other Tyrant-type monsters, Nosferatu's weak point is its exposed heart.

Steve Burnside Tyrant

Steve Burnside became a Tyrant himslef once he suffered the exact same experiment Alexia Ashford did on her Father, Alexander Ashford, receiving large doses of T-Veronica virus. Due to him being exposed to this virus for such a brief period of time, it is believed he was still able to conciously fight against its intrusion on his brain. But the only way to trigger this is to expose him to supreme mental vexing, such as seeing a good friend in mortal danger. Further information: Steve Burnside,

Alexia

The main boss of Resident Evil: Code Veronica. In her first form, Alexia retains a mostly human form, with the exception of of the green muscle extending up and down her right arm and her left leg, and she's able to retain her complete human intellect. Her blood, when it contacts air, bursts into flames. In her second form she is like an ant queen with a giant lower body where she produces partially formed larvae. In her third and final form she is most like an insect. She has four wings and a peculiarly shaped tail. This third form is destroyed by Chris Redfield at the end of the game.
Appearances: Resident Evil: Code Veronica

Bird-based creatures

Crow

During the initial viral outbreak in the Arklay Mountains, as well as in the later outbreak in Raccoon City, most of the crows were immediately infected with the T-Virus after eating the dead meat of an infected creature(alive or dead as zombies are immune to pain). An infected crow might resemble a regular crow at first, but will immediately attack any living creature that wander into its territory with their sharp beaks. Also, an infected crow is not as sensitive to loud noises as their regular counterparts.
Appears in: Resident Evil 0, Resident Evil, Resident Evil 2, Resident Evil 3

Insect-based creatures

Wasp

Bees thriving in the Arklay Research Center's Residence, that have grown to a huge size thanks to the viral outbreak. They hold difference from a normal bee except for the size, but they do build a massive hive in the house, from which they have to be smothered with pesticide.

Large Roach

They appear only in one area in resident evil 2, making them rather an obstacle, than a real enemy. The move slower than a running character, so fighting them is not really a case.

Ant

A small insect that poses minimum threat.

Moth/Moth Giant

A large moth. During Leon's travel to the secret lab, he had to take care of one of these, which nested itself in a the fingerprint computer-registering security room.
Appears in: Resident Evil 2

Plague Crawler

The Plague Crawler is one of the bio-weapons created from James Marcus' early experiments with the T-Virus, along with the Eliminators and Lurkers. They were created by manipulating the genes of several bugs into one organism and then implanting into the virus. A Plague Crawler is two meters long in size and attacks its prey with large pincers. They were considered unfit for heavy combat due to their lack of intelligence and were disposed. However, a few of the specimens survived and managed to procreate outside of human eyes.
Appears in: Resident Evil 0

Brain Sucker

The Brain sucker is a relative of the Drain Deimos. These creatures mainly differ from Drain Deimos by their attacks. These creatures run at you and try to latch on to you. They do this to suck your brain of blood. Sometimes while in the process of doing so they inject you with a poison.
Appears in: Resident evil 3

Drain Deimos

Fish-based creatures

Neptune

Neptune (named after the Roman god of the sea) is a B.O.W. that was created by implanting the T-Virus into a great white shark. It was given the development code of Fi-3 and was created specifically to test the effects of the virus on a sea creature. The creature was accompanied by two smaller offspring. During the viral outbreak in the facility, Neptune and its spawn were released from their water tanks by a mad scientist, flooding the entire Aqua Ring. The creatures are very persistent and dangerous underwater. Instead of confronting the two first sharks directly, one must go to the water control room and activate the drainage system. Once they're out of the water, they become completely vulnerable to gunfire or electrocution. Then to deal with the last one one must push a power box into its tank, killing it instantly.

Reptile-based creatures

Alligator

During the viral outbreak in Raccoon City, survivors Leon S. Kennedy and Claire Redfield encountered an Alligator that mutated to large size as a result of T-Virus exposure. The creature most notable characteristics includes its huge size (over ten meters long) and its craving to bite anything. It uses the trash dump inside the sewers as it habitat and source of food.
Infected Alligators were also seen during the viral outbreak in Sheena Island. Like the one in Raccoon City, these were not deliberate bio-weapons, but accidental creations.
Appears in: Resident Evil 2, Resident Evil Survivor

Yawn
Yawn, the first boss in the original Resident Evil. The Yawn is a snake-based B.O.W. that was originally a specimen that escaped from the laboratory and grew to large proportions as a result of exposure to the T-Virus. It got its name from the lab's researchers due to the fact that it appears to be yawning before swallowing its prey. Yawn's most distinguishing characterisitics is the inconsistency between its width and length. Its movement and attack patterns resembles a regular snake. However, its fangs are coated with a potent venom that can only be treated with an unsually powerful serum found in the mansion's medical storage room. If the wound is not treated on time, the victim will be immobilized and eventually killed by the poison.
During the mansion incident, the members of S.T.A.R.S. Alpha Team confronted this creature inside the mansion's attic. Prior to that, Bravo Team operative Richard Aiken was already wounded by the snake and warned the team before the battle. The team managed to fend off the creature. The second and final battle ocurred in the mansion's piano lesson room (or in the library in the GameCube remake), however the snake was wounded from the previous battle and was easier to dispose of. Alpha Team was abled to neutralize the creature with no problem. In the recent Resident Evil: Deadly Silence remake for the Nintendo DS, a second Yawn is discovered in the same room where players earlier battled Plant 42. Unlike the earlier Yawn, this version has improved skin, making it invulnerable to damage except for its soft underbelly and mouth. Players must have quick reflexes with their knives in order to defeat this improved Yawn.
Adder

A small snake that was not mutated extensively by the T-Virus, and that holds none of the characteristics of more enhanced B.O.W.s, such as Yawn. However, it retains poisoning capabilites and some agility in combat, in addition to being hard to hit.

Leech-based creatures

Mimicry Marcus

Leeches infected with the T-virus become increasingly agressive. They also seem to posess a collective intellegence, and often seem to act as a single entity. When a large enough brood of leeches come together, they assemble into a humanoid form. Named mimicry marcus dues to its alikness to James Marcus. Its arms and limbs can extend to strike at targets at a massive distance away. If it can manage to grab a hold of you it will soak you with an acidic secretion. It is so resilient that it will survive having its head and arms completely blown away. In doing so, it will swell to an enormous size, back the hero into a corner, and explode causing massive damage. The mimicry marcus is also very susseptable to fire and, rather than exploding, it will simply dissolve if attacked with a flame based weapon like a molotov cocktail or napalm grenade.
Appearances: Resident evil 0

Queen Leech

This resident evil 0 boss is basically a giant human shaped leech. It has control over all other leeches. The queen leech has a second form in which it loses most of its human form to become a massive green creature. The queen leech is also, importantly, repelled by light.
Appearances: Resident evil 0