Just wanted to list some features of DoW's Hell and its demons to compare with other invasive scifi factions, such as the Flood, Zerg, Necromorphs, any of the W40K species, etc.

Strengths:

Supernatural power is inherently superior to purely physical forces. Demons have much higher defensive/offensive capabilities than equivalent mortal opponents, with only the weakest of demons even being vulnerable to mundane factors/weaponry. Demons are capable of surviving in virtually all physical environments without the need to adapt. Furthermore, they have incredible regenerative properties and can naturally heal even the gravest of injuries over time, though this can be accelerated by preying on other beings or even by their own power. All true demons are inherently immortal. Even if their physical bodies are completely destroyed, demons' souls persist past death and can freely reform a body from their native Hellscape or even physical surroundings. The only way a demon can be permanently stopped is by intense psychic attack of great power, shattering their spirit so thoroughly that they can never reform, which becomes more difficult on higher demons. Besides just sheer offensive/defensive potential, all demons also host a wide array of supernatural abilities allowing them to freely bend, shape, and corrupt both the physical and metaphysical reality of Hell and our universe. And while demonic technology varies greatly across assimilated or native civilizations all the way up to the Fallen Hosts, it is generally far superior to those of most mortals. All demons also possess a wide array of psychic powers, allowing them to torment, anguish, confuse, mislead, brainwash, control, even destroy other minds. They can instantly transmit and receive commands and information across vast distances of space and time through telepathy, letting entire legions coordinate and move as single units under the command of their lords. While not all demons are conscious, even the lowliest warriors possess basic tactical intelligence, while demon lords are highly intelligent. Some also possess the ability to absorb knowledge directly from mortal minds or that which is imprinted onto their technology and environments, letting them understand and interact with these. Hell's reality is home to unimaginably powerful beings and forces, far greater than those that exist within our universe and arguably perhaps anywhere else. Demons exist only for the sake of chaos, destruction, and evil. They are not restrained by mortal concepts such as empathy, compassion, remorse, pity, or mercy. They are not even concerned for their own survival. Hell has the ability to corrupt and assimilate any and all mortal beings, turning them into servants for the demons and blessing them with dark magic for the purpose of carrying out Hell's wishes. These beings become as zombies, granting the use of their minds, bodies, knowledge, and technology to their demonic masters. These corrupted beings are exploited and used to act on the behalf of true demons where they are unable to, moving across the universe and even across dimensions to the command of their masters. While Heaven opposes Hell's advances in the Immortal Realms, Heaven is restricted in its capacity for action in the mortal universe by doctrine and dogma, along with a generally hands-off approach and reclusive nature. Hell and demons are not bound by physical factors such as resources or sustenance. Demons derive their strength and power directly from Hell, using mortals only as pawns. This also means that the numbers of demonic forces are, for all purposes, infinite. Hell's one advantage over the Doom Slayer is that there is only one of him and he can only exist in one place at a time, while Hell's evil is virtually omnipresent and its numbers infinite. And although they can't kill, corrupt, or even stop the Doom Slayer (at most only slow him down) they could kill every other human in existence and thus strip him of his purpose and will to fight, which is presently considered the only way to truly defeat him.

Weaknesses:

The nigh-impenetrable Murus Dei separates Hell from the rest of Creation, making it almost impossible for all but the meagerest of demonic forces and beings to breach through. Because of this mystical barrier, demons find it difficult to coordinate invasions even once breached into our universe. They must build Gore Nests as means of communication and reinforcements across dimensions, and their invasions must be commanded by some type of infiltrated lord or commander to be effective. These are thus points of vulnerability in demons' chain of command and their destruction would critically undermine their invasion. Our universe is fundamentally different from Hell's reality, making it incredibly difficult for true Hell-native demons to understand and hence exploit. And since only the weakest (and dumbest) demons find it relatively easy to break through, they are at a clear disadvantage in our reality, vulnerable to being outsmarted even if by physically inferior mortals. Some demons are simply incapable of learning about or understanding our reality. Dimensional space-time is a factor of our physical universe, not existing within Hell or the other Immortal Realms. While this has unique advantages to Immortals such as demons, it also poses unique disadvantages because they can become disoriented or even lost in the probabilistic wavefunctions of higher dimensions, pointlessly navigating infinite "imaginary" timelines while the "real" timeline remains unaffected. Since the higher powers of our universe are not limited in their reach as demons are, most demonic incursions can be reasonably contained and neutralized before they become a threat to the greater cosmos, partly because most infiltrated demons are weak to begin with. These powers prevent demons from travelling even just between planets without the use of shielded starships or other contained transportation vectors, critically limiting the speed of their propagation compared to what would otherwise be possible. This does not mean that mortal civilizations affected by invasions will survive, however. Because Hell's reality is of pure chaos and evil, it is in all demons' natures to oppose and fight each other, either to eliminate rivals, increase their own rank, seek advantages for themselves, or simply just for the literal Hell of it. This lack of unity and coordination stretches all the way to the highest tiers of demonic hierarchy, undermining their full potential as is but proving vulnerable to exploitation by clever mortals as well. Demon lords must constantly use their power to enforce their command and guard of threats from other rivals or even their own masters. And if said lords are eliminated, it is not uncommon for entire demonic legions to fall to ruin and infighting. Hell is eternally rivaled and opposed by the forces of Heaven. While Heaven is not as large or expansionist as Hell, its subjects are just as powerful, perfectly unified in their goals, and not restrained by the Murus Dei. Even "lesser" mortal minds possessing psychic abilities themselves can infect the minds of demons. Although they may be objectively weaker, mortal minds are fundamentally different and alien to those of demons and can instill unique concepts or experiences that can drive demons insane, up to even breaking their souls, so to speak. Because demons have no fear of death or pain (besides before the Doom Slayer), existing only for the sake of chaos and destruction, they can and frequently do fall into losing battles against stronger opponents. The one known as the Doom Slayer is the sworn enemy of Hell and all demon-kind, vowing to "rip and tear until it is done." He is an immortal, unstoppable, incorruptible, invincible warrior that only grows more powerful with every kill, and the only thing they truly fear. There is no ground he would not tread, no monster he would not fight, no being he could not kill. His entire purpose is to protect his people, the human species, from complete annihilation at the hands of demons.

It is not known if the Slayer has found a way to conceal his home world or if he has exterminated all that knew of its location, but it is understood that the Slayer's home planet is off-limits to demonkind or any other alien species, and to intrude on the Slayer's domain is to risk bringing down his legendary wrath.