Dead Space: Downfall is a Direct-to-Video Prequel to Dead Space set in the Dead Space universe. It goes into detail about what happend onboard the USG Ishimura and the state it is in when Isaac Clarke and the player reach it at the beginning of Dead Space.The Red Marker is brought onboard the Ishimura. Meanwhile the colony on Aegis VII is attack by Necromorphs. One of the colonists escapes with the corpse of his dead wife and heads to the Ishimura, unaware that his wife is turning into a Necromorph. Onboard the Ishimura, the Unitologists want to worship the Marker, and start to otherwise go insane.The colonists ship crashes into the Ishimura and the Necromorph escapes, eventually making its way down to the morgue and inficting all the bodies down there. A team of crew members, led by chief of security Alissa Vincent, try to fight their way from the morgue to the top of the ship.
Dead Space: Downfall provides examples of the following tropes:
Accidental Murder: Dr. Kyne's attempt to sedate Captain Mathius goes horribly wrong, ending with the Captain dying. The crew members (who had been restraining Mathius after agreeing with Kyne's assertion he was unfit for duty) wonder aloud whether or not it really was an accident; Kyne flees the bridge before he can be detained.
Apocalyptic Log: The log Vincent records explaining what happened on the ship.
Black Dude Dies First: Averted. Pendleton may be black, and he may have gotten killed relatively quickly, but he's still not the first person of the Five-Man Band to bite it. Hell, he's not even the first person in the movie to die on-screen.
Call Back: At the very beginning of the movie, the first thing you see is the back of an engineer wearing the same suit as Isaac. It looks almost like a shot from the original game, complete with camera angle.
The Cameo: Nicole has a non-speaking appearance, being rescued by Vincent with some other civilians.
Continuity Snarl: The movie timeline runs much faster than is implied to have happened in the game; the game's audio logs suggest the Sanity Slippage took days to manifest alongside the Necromorphs. Other differences include the Marker being much larger and the Necromorphs being unable to approach it. Though that may be because it has use for Vincent.
Downer Ending: Everyone is killed and the Ishimura is a death trap.
Eye Scream: In the games, you only saw a video log of it; in the movie, you get to watch Mathius get stabbed in the eye up close. Then it goes further into this when after he gets impaled in the eye, he falls onto the floor, driving it into his brain.
Face Death with Dignity: Samuel Irons. As the Necromorphs advance on him, with his plasma chainsaw no longer functional and his strength depleted, he simply takes his Unitologist pendant and recites a prayer before being hacked to death.
Flipping the Bird: Vincent gives Mathius a salute with her middle finger, though his back is turned at the time.
Foregone Conclusion: Even when the movie takes a few liberties with the plot, anyone who has knowledge of the game knows how this will end. Everyone dies and the ship is lost to the monster infestation. Even the opening scene lays it all out by showing Vincent's final recording declaring her the only remaining survivor.
Guns Are Useless: The security team's sidearms do precisely jack against the Necromorphs. Justified, since it's an established fact from the games that tactical dismemberment does a better job than conventional shooting.
Heroic Sacrifice: Both Irons and Ramirez know they're going crazy, so they go out fighting instead. Vincent gets sucked into space when she opens the docking bay so she can launch the emergency beacon on the shuttle.
Honor Before Reason: Vincent's attempts to stop Kyne are intended to save the crew, who are rapidly being butchered by Necromorphs. Hell, by the time she gets to him, there can charitably be said to be maybe a dozen left.
How We Got Here: The movie starts as Vincent is recording her log, then flashes back to how everything started.
Obligatory Swearing: The characters in the movie are a lot more swear-happy than the characters in the video game.
Off Model: The health bars on everyone's RIGs are almost never consistent, let alone move down. Mathius' is a notable aversion to this, since we see his health meter quickly drop after the event listed under Eye Scream.
Oh Crap: The patient from the mining colony gets one when he finds out the monsters from the colony have ended up on the ship.
Only Sane Man: Kyne (for a given definition of "sane"), and to a lesser extent Vincent. Both are the only two characters to remain completely rational throughout the film. Vincent gets a lower rank because she's a bit too Genre Blind for her own good (or that of others). She only comes to her senses after having sabotaged Kyne's first attempt, and by then it's too late.
Shaming the Mob: Samuel Irons breaks up an angry protest by the Unitologists on the Ishimura who're clamoring to see the Red Marker. One reasonable speech later, he's convinced them to improve the public perception of Unitology by not rebelling against the captain's orders and leave the Marker alone until they get permission to view it.
Tempting Fate: Lampshaded when Vincent remarks on Hydroponics seeming to be clear.