Mancubus

The Mancubus is a cyborg demon found in the DOOM Universe, and has a few distinct subspecies. The Manucubus is rather slow moving due to its size, but what it lacks in speed, it makes up for in the damaging effects of its projectiles.

Biology
The physical features of the Mancubus consist of a large, morbidly obese build, a large bloody mouth with sharp teeth, and twin cybernetic flamethrower appendages, connected to a fuel tank grafted onto its back, with tubes connected to its skin via tubes of the creature's own flesh. The cybernetics on its arms left sickly distinctions where flesh meets machine. Its skin is of a lighter brown complexion, and does not contain any visible body hair. The original, fully organic appearance of the Mancubus is unknown, but it is assumed that the Mancubus had humanoid lower arms and hands. It has two green eyes that lack pupils, and its legs resemble those of elephants, bearing six toes each. The Mancubus has three known subspecies: Trunked Mancubi, Cyclops Mancubi, and Didactyl Mancubi. The Trunked Mancubi bears a similar appearance as a morbidly obese humanoid, although larger, and bears a large trunk, with two feeding appendages next to its trunk. Its eyes are all black, and its skin is grey. It is possible that another demon known as the Vagary, a female semi-humanoid arachnid demon, is the "mother" of the Trunked Mancubi, as Vagarys carry a malformed Trunked Mancubus fetus within their bodies. Their cybernetic flamethrowers appear somewhat old and rusted, but still function properly. Cyclops Mancubi are pink skinned, also larger than ordinay Mancubi, and equally obese. Their defining trait is their green cyclopedic eye over their mouth of sharp, rotting teeth, and their ability to naturally grow biomechanical flamethrowers when they reach maturity. While juvenile, Cyclops Mancubi presumably have humanoid hands, and gorge themselves on meat. As they reach maturity, a chitinous growth forms over each hand, eventually creating their flamethrowers. Their hands rot away, and the rotting material creates the fuel needed for their flamethrowers. In addition, they appear to grow some natural armor, but their obese frames quickly expose their bellies and heads as they outgrow their armor. These Mancubi appear somewhat artificially modified, and their natural ability to grow flamethrowers and armor could be the result of being bred for war or previously modified by demonic commanders. Their intestines and other organs are known to be explosive, and will combust if pierced by weaponry or otherwise pulled out. Their innards also appear to resemble those of Gore Nests, although any relation between the Mancubus and Gore Nest is unknown. The last known subspecies of Mancubi is the Didactyl Mancubi, which better resembles the original breed, with the exception of only bearing two toes per foot and having a pale pink skin tone, while also appearing to be covered in scars or vein-like protrusions, with two defined tusks and yellow eyes. Their cybernetic flamethrowers consist of an inner fireball cannon and an outer barrel, which enables them to spew a continuous plume of fire, unless destroyed. The fuel tank on their back appears to be grafted into their spine, and they also appear to bear an additional heart-like power source in their chest, which will also explode if removed or punctured.

History
The Mancubi (plural) came from a demonic dimension called Hell. Throughout an unknown period of time, various subspecies of the Mancubus arose, and were used as soldiers in interdimensional invasions, often fighting a race of Humans known as Argenta, led by the Order of the Night Sentinels. The Argenta priests turned against the rest of the Argenta, siding with the Maykrs, who struck a deal with Hell for their mutual benefit. The Night Sentinels, along with their champion, an unnamed human known only as the Doom Slayer, were trapped in Hell, where Mancubi and other demons launched a relentless assault on them. Only the Doom Slayer survived, and continued to fight demons for eons, until he was finally locked away in a tomb on the surface of Mars within an unknown universe. At some point, demons either developed or stole cybernetic technology, and modified Mancubi to have flamethrowers for arms. In the future, when Union Aerospace Corporation (UAC) scientists were experimenting with teleportation technology on Phobos, they accidentally opened a rift to Hell. This caused a whole manner of demonic forces, including the Mancubi, to come through the portal onto Mars' moons and the other bases. The demons brought destruction on the UAC bases and killed or possessed many UAC personnel. Not too much later, they made their way to Earth to continue their attack there. A group of Mancubi was tasked with holding an Earth spaceport hostage, as the port held a control unit that would allow Human star cruisers to get away from Earth and the invasion. It was here that a single hero, a marine, slaughtered the demon hordes, including Mancubi, allowing Humans to escape, and later managed to close the rift between the dimension of Hell and the Earth itself, sealing surviving Mancubi away in Hell. The corpses of Mancubi left on the Martian moons would later be revived by the Mother of All Demons, only for the marine to destroy them again. The marine then voluntarily remained in Hell to put down its threat forever, fighting hordes of demons alone, somehow going back in time and across dimensions, eventually becoming the immortal superhuman known as the Doom Slayer, the very one who had fought demons over eons. Some time in the future, in what appears to be another universe, a trunked subspecies of Mancubi was among an invasion force that attacked a UAC Mars base, brought over by a human cultist named Dr. Betruger. An unnamed UAC Marine fought his way through the Mancubi and other demons to Hell, killing the Cyberdemon and stopping the invasion. At another point in the future, in what could be the same universe, Mancubi were brought to Mars, kept in captivity, and studied by a growing faction of cultists within the UAC, led by Dr. Olivia Pierce. These Mancubi were of a cyclopedic subspecies, who naturally grew flamethrowers and armor, and many of their number were cybernetically modified with UAC technology into the formidable Cyber-Mancubi. When the demons launched another invasion of Mars, the Doom Slayer was woken up, as the universe he was held in was the very one being invaded. Retrieving his armor and weapons, the Doom Slayer eventually fought Cyclops Mancubi and Cyber-Mancubi alike, killing them and other demons, eventually killing the Spider Mastermind and stopping the invasion. Years later, in the same universe, a demonic invasion of Earth was launched at the order of the Khan Maykr, and Doom Slayer, who had been banished out to unknown regions of space at the end of the previous invasion, returned in an Argenta space station to combat the demons once more. This time, the Didatcyl Mancubi subspecies were used, some of which were also modified by UAC cultists into a new breed of Cyber-Mancubi, who fought alongside other demons against the Armored Response Coalition (ARC), Earth's current defense force, and UAC security forces not loyal to the cultists. Many were killed in Slayer's rampage throughout Hell, Earth, Mars, and Urdak. All Mancubi remaining on Earth were killed or otherwise banished after the death of the Icon of Sin. Slayer then utilized ARC resources to retrieve the life sphere of the Dark Lord in order to destroy it, killing more Mancubi along the way.