- The Scrin. Peptuck has said that he wanted to make it clear just how terrifyingly powerful they are compared with everyone else, and IT. IS. WORKING.
- The Scrin have apparently gone to work on the husks in the same way the Geth did in the original game. Instead of an electrical blast, they're now armed with energy cannons on their arms, and their hands are four foot long blades.
- Buzzers. Everything about the Buzzers. They swarm you en masse, break into your armor, and then chop anything organic they find into soup. In seconds. Shepard herself is completely terrified of these things, and with good reason. Going by her flashback to Akuze, there was a Scrin Buzzer cutting up through her nose. Her dream in "Ghosts" takes their nightmarishness to even greater heights, because she gets attacked by a swarm of them and, unlike in real life, doesn't die. She's just lying there, getting sliced to pieces bit by bit by the swarm while the vision progresses.
- Ravagers. Shepard pumped an entire clip of grenades into one, and it still just kept coming. *shudder*
- The Battlemind. Unrelenting, and nearly unstoppable (to the point where an entire belt clip of sonic grenades - the Scrin's Kryptonite - detonating on top of it merely stuns it) and armed with a weapon that lets it tear apart walls and vehicles and infantry squads with casual ease. And on top of that? It has a sense of humor.
- The Scrin cruiser that defeated the turian cruiser Valadictum. It effectively tanked everything the turian ship threw at it while firing back tiberium-tipped directional flak shells loaded with nuclear explosives. And then it casually outmanuevered the Valedictum, disabled it, and instantly took control of the entire crew with Masterminds.
- When Kane showed up at the end of chapter five, the fanbase was roaring their approval, anticipating that the Tiberian Saga's favorite Chessmaster, Dark Messiah, and all around Magnificent Bastard would start playing everyone like a piano. And then, in the very next chapter, after doing just that to the entire Citadel Council chamber, with Shepard tailing him after he makes a discreet exit. In the ensuing conversation, Kane says three little words that made the fanbase's collective hearts stop beating: "I don't know."
- From Chapter 14, we have Shepard's Tacitus-induced nightmares/visions. A lot of people dying horrible deaths at the hands of the Scrin, the Reapers, and even by a Prothean's hand. Also? The Collectors have begun their assault on humanity early.
Nightmare Fuel / Renegade