The Mass Effect series is a science fiction adventure that takes players on a fantastic journey, visiting all the wonders (and dangers) of the galaxy. However, this doesn't mean there won't be some absolutely traumatizing events that might mentally scar you for life, especially since the the main villains take the plot to Cosmic Horror Story levels. Here you can find some of the most frightening and pants-wettingly terrifying horrors of the years 2183-2186.
- Mass Effect: Retribution has a few genuinely creepy parts, mostly because it explicitly spells out what indoctrination is like. The Cerberus experiments on him involving implanting Reaper nanotech having taken And I Must Scream to new levels, Paul Grayson spends entire chapters desperately trying to exert some kind of control over his body, trying to stop himself, move a muscle, anything- but the Reapers are so skilled that they quickly find ways to keep him incapacitated. By the end, he's trapped within his own body, the Reapers having full control over his body and full access to his memories. Fridge Horror kicks in when you realize this matches the exact same description Matriarch Benezia gave of her indoctrination. ("I am NOT myself, I never will be again!")
- What makes it worse is how subtle the Reapers are when they're controlling him. He tries to resist them and commit suicide, and is able to resist a direct effort to control him, so the Reapers instead subtly manipulate his emotional centers to make Grayson decide that suicide is a coward's way out, and instead he seeks help from Kahlee to fight the infestation - which is exactly what they want. In other words, they manipulate it so that Grayson's decisions on how to fight back against them helps the Reapers achieve their goals.
- Hilo'Jaa vas Idenna being described after he was interrogated by Pel in Mass Effect: Ascension. He was beaten, cut, burned with acid, had his teeth pulled out, had his eyelids ripped off and one eye was swollen, fingers broken, and had contracted an alien disease that caused some growth to come out of his wounds. And he was still alive when Grayson found him.
- Kicking off the beginning of the Reapers' invasion after Mass Effect 2: Arrival, Mass Effect: Invasion introduces us to a whole new type of Husk called Adjutants. These creatures were created by Cerberus in an effort to better understand Reaper technology and use it against them. Unfortunately, the Adjutants escape, hijack some ships and raid the Omega space station. With every kill, they assimilate the corpses which, in their own horrific way, rapidly change with newly grown wires, converted flesh and reassembled bone structures into other Adjutants, no matter the species. Spreading like a plague mixed with wildfire, the crime boss Aria has to deal with the Adjutants before they take over the entire station and possibly escape beyond the star system. [To make it worse, it's confirmed TIM intentionally released the Adjutants just so he could take control of Omega.
- From The Alliance News Network: While the stuff about even the Geth getting in on the fun, kicking the Batarians when they're down is somewhat hilarious... there's a little titbit from before that which is truly horrifying and depressing: Apparently, most Alliance soldiers don't even bother to shout warnings to Batarian soldiers when they've noticed there is a freaking Banshee behind them.
- The games made clear how dreaded and dangerous a powerful biotic can be as an enemy. There's three different stories of a biotic destroying entire space stations. Two of them are offcreen and involved a fight between a Krogan and an Asari biotic, and you can follow the results of the third: once Shepard released Jack from cryo, she proceded to tear apart the station.