We open in Hell, before a vast Hell Gate. A LEGION of demons; imps, pinkies, knights, etc. are assembled before the Gate. A pair of hands rises up in front of the POV, and we see that we are watching this through the eyes of a demon, likely another imp. A monstrous horn bellows out as the Gate surges to life with a crackle of blood-red lightning. The demons CHARGE, pouring through the gate, their bloodlust visible in their frenzied body language and howls of sadistic glee.
Our POV Imp rushes through the Gate, and in a flash we're in a UAC Facility. Alarm klaxons ring out, UAC peons stumble about in a panic.
"Attention! Portal Malfunction. Demonic Invasion in Progress." States a mechanical female voice, impassively.
The POV Imp rushes at the nearest human, an unarmed scientist who lets out a cry of terror just as the Imp RIPS his arm off and smacks him aside with it. Other demons rush around, and our POV Imp turns to watch a few vicious kills from some of the demons around him. Some of the humans even kneel over pentagrams, willing sacrifices for the demons, whom they gleefully kill without bias.
The POV then takes on a Video Game style; a Health Bar appears, the Imp switches between Claws and Fireballs, which are on a quick, half-second cooldown function and otherwise have unlimited ammo. Humans run all around, some flashing the tell-tale glimmer of an impending Glory Kill. The Imp hurls fireballs and slashes unarmed humans, then security forces enter and start shooting, and the POV Imp ducks, weaves, hangs from walls and fireballs his way to dominance over the meager human forces. In short order, all the humans in the area are dead.
Suddenly an EXPLOSION rips through the area! A cry of terror wells up not from the humans, but from the Imp's fellow demons. Gunshots run out, and the lights wink out, leaving the room in darkness save for the spinning red light of an alarm klaxon. The Demons scatter, and our POV Imp leaps up into a vent, scrambling through the duct system. As it passes by vent grills we see hints of SOMETHING fighting the Demons--and winning. We hear the blare of a shotgun, the rapid fire of a machinegun (and bullet holes punching through the vent our POV Imp is hiding in), explosions from grenades and the electronic hum of a plasma gun.
Now it's quiet, and the Imp crawls out of the vent into a darkened hallway full of smoke and sparks. It's breathing is heavy and fearful, its demonic hands shaking as it passes by the corpses of its fellows rendered into so many gibs on the walls and floors. A flash of light from further ahead and we see a Hellknight bellow it's last as a shadowy, hulking figure cracks its neck like dry twigs and then vanishes back into the smoke. Our POV Imp rushes forward, hurling balls of flame, but the attacker is gone.
A chainsaw REVS. The sound seems to come from all directions, and then there's the HEAVY THUD of armored boots charging down the corridor. A hint of green comes from the darkness and the Imp hurls a ball of flame, illuminating the DOOM MARINE, who charges right through the fireball without slowing. He raises his chainsaw and KICKS the Imp hard, knocking it back, bringing the Imp's Health to 25%. The POV Imp feebly tries to block the Marine with its arms, who brings the Chainsaw down through the Imp's limbs, sawing them off in gory fashion before our very eyes, and as the blade cuts through and reaches the Imp's head it strikes the camers and SMASHES it in a shower of glass and blood! The title "DOOM" appears, frozen on the broken image of the Doom Marine in mid-kill.