* Despite the Tenno who gain their insane powers from the Void, the place where logic fails, there are things like Stalker, the Grustrag Three or the Lephantis. ''There are even more bigger fishes than these super-soldiers.''
* [[AndIMustScream Let's just say that you don't want to fail a Rescue mission by time out]]. The fact that it was audio only doesn't help.
** In a similar vein, the way Capture targets howl in pain as you capture them. Were it not for the ''Stolen Dreams'' quest, you could be forgiven for thinking you were subjecting them to a FateWorseThanDeath simply with the "teleportation", especially since the Grineer have already proven faster/less painful teleportation technology exists.
* The Stalker, if you aren't expecting him. You're out, minding your own business, celebrating a boss' defeat, when suddenly, the lights flicker. Then:
--> '''Stalker:''' [Player], you cannot run from your past.
* The [[{{Precursors}} Orokin]] [[EldritchLocation Void]]. Pristine. Beautiful. [[LostTechnology Transcendant]]. Utterly empty except for "corrupted," nearly-silent versions of enemies you face in normal levels. [[NothingIsScarier No music plays during these levels]]. Look out a window and all you'll see is black dots in an endless white expanse. It begs two questions - who were the Orokin, and where did they go?
* The Zanuka Project: various sliced-up Tenno and their warframes formed into a mechanical quadruped controlled by Corpus technology.
* Valkyr, the Warframe produced as a byproduct of the Zanuka Project. All subsequent Valkyr frames are based off of the template of the original. It's impossible to tell what frame Valkyr used to be, or if we've even seen it yet, but that's not even the scariest part. Given that Warframes draw their power from the [[EldritchLocation Void]] in a manner that is suggested to be intrinsic to their psychology and outlook on life, it suggests that whatever Alad V [[ColdBloodedTorture did to Valkyr]] caused her psychology to [[MindRape change so drastically]] it ''altered her Void imprint''.
* The Infested. Grineer and Corpus alike who were unlucky enough to get infected, twisted and hideously mutated. Some wind up running on limbs that used to bend the ''other'' way; others as eyeless things with no purpose but to get close to an enemy, at which point they spasm and then ''explode'' in a spray of gore and nano spores. Some are reduced to just a (mostly) headless torso, pulling itself along with its flailing arms. ''Pray'' that nothing of the original mind remains.
** The [[http://static2.wikia.nocookie.net/__cb20131207105127/warframe/images/9/90/RunnerDE.png Infested Corpus]] have a new arm growing from their chest and fused to their face and helmets like it was grasping at their skulls. The [[http://static2.wikia.nocookie.net/__cb20131207105127/warframe/images/thumb/5/5a/ChargerDE.png/250px-ChargerDE.png Infested Grineer]], once humanoid, have been twisted into quadrupeds in the grossest way possible, their chests pointing up in the air with their limbs bent backwards and joints inverted, a new "head" forming over their heart while their old skull hangs below their body. As for the [[http://static2.wikia.nocookie.net/__cb20131207111710/warframe/images/thumb/6/69/ToxicAncient2DE.png/250px-ToxicAncient2DE.png Ancients]], whatever they were before, they have no resemblance to it at all now.
** Lephantis, a bio-engineered Infested monstrosity that was created for the Old War and survived by hiding in a derelict [[{{Precursor}} Orokin]] ship. It consumed and absorbed everything and everyone that discovered it, and so when you reach its chamber, it attacks you with giant, twisted versions of all the enemy factions. The Corpus head is especially horrifying, as the infested Crewman's helmet has fused with his skull and become a mouth that opens to attack you (compare [[http://img4.wikia.nocookie.net/__cb20140330082122/warframe/images/9/9a/CrewmanDE2.png a normal Crewman]] to the [[http://img3.wikia.nocookie.net/__cb20130920113215/warframe/images/8/80/2013-09-20_00021.jpg mutated version]]), and the Grineer head has a huge scythe which is basically an instant kill. [[spoiler: When you defeat the heads, the floor beneath you breaks, and you fall down to see Lephantis's main body, a building sized monster with all three of the heads growing out of it. [[OhCrap Only then does the boss subtitle appear.]] ]] Doesn't help that all the while, Lephantis is [[ItCanThink sending you messages]] like ''"We are countless. Consume us. Be reborn."'' and ''"We embrace you. Why do you defile us?"''.
** One has to look at Infested rescue mission to see [[ItCanThink how smart they were.]]
** At the first day of Warframe, planet Eris was described as the location of far-flung Corpus outpost. Now, every single mission nodes there are controlled by Infested.
* [[http://www.youtube.com/watch?v=wOygJJ7Zudk Vay Hek addresses the Tenno directly.]]
** The fact that the video appeared exactly at the end of a developer livestream interrupting it mid sentence without warning increased the effect.
* Before the Grustrag Three show up, the Lotus contacts you about 'impossible readings' she is picking up nearby, and her transmission is abruptly cut off. She gets out a few more garbled transmissions about how you are 'being hunted' and then suddenly begs the Tenno to abort the mission ''now'' before she is cut off totally. [[NothingIsScarier There's a few seconds of nothing]], then the Three spawn into the level.
** The ''genuine concern'' you can hear in her voice is what really frightened me the first time the Grustrag Three appeared in my game. Lotus, while she does care, is nothing but utterly calm, or at most, mildly surprised, even on the most dangerous missions. Suddenly, she is clearly frightened and confused, screaming at the player to abort and ''run'' before getting cut off.
** Seeing your Warframe getting captured under the orange cage-things is pretty disturbing too, double if you don't know what's happening.
* Infested Corpus Ships. They have [[https://www.youtube.com/watch?v=eMUkXQ31q9g this music]], are claustrophic, full of deadly hazards that get worse as you kill more hive nodes, near-insta-kill poison enemies can trap you at close range, and there are so many infested in your face that you ''will'' start drowning in them if you don't have a decent piercing or crowd-control ability. All that's missing is the M41A Pulse Rifle.
** Sometimes an Infested Charger can burst out of a vent next to you, Franchise/DeadSpace style, [[ParanoiaFuel even if you're on an Exterminate and have killed all the enemies.]]
* Vor's ominous threats and taunts as [[spoiler:his Ascaris slowly takes more and more of you over]] in Update 14, culminating in this line that replaces the Lotus' standard "Mission complete" dialogue at the end of the Corpus Hijack mission.
-->You are '''MINE'''.
* Story-wise, the little information we have of the Sentients leans them towards this. These are something so threatening that the Orokin unleashed the Technocyte Plague and the Tenno in order to try and stop it. They pilot "worm-ships" which use heat-bursts to boil their enemies from the inside, are described as having "multi-faceted eyes", and are nearly endless in number.
** [[FromBadToWorse It Gets Worse]]; The Tenno were chosen to be used in the war because their powers were spawned from the void-- a "hellspace where science and reason failed"-- and thus couldn't be subverted by the Sentients, who were getting stronger with every advance the Orokin fielded. Lotus reinforces this in Vor's Prize, pointing out that the presence of the melee weapon was an adaptation to the sentient's ability to subvert technology.
*** Ember Prime's codex entry implies that the Orokin were so desperate that they even [[spoiler: threw ''kids'']] into the Void.
** The Tenno themselves. Almost completely silent killers, who can strike almost anywhere and at any time. Their nature is largely unrevealed as well. All we know is that those who made it back from the void [[CameBackWrong came back wrong]]. High ranking Tenno can and will single-handedly wipe out entire armies, from lowly grunts to the elite of the elite. The only enemy who regularly gives a well equipped Tenno pause is the Stalker.
* What happened to the original Limbo. Specifically, the way it's described to us.
-->'''Ordis:''' Oh, wait, Limbo, no that's a mistake, you don't want to go there. It's too big a jump. You can't rift walk... ohh. Oh no. Operator, I think I know [[TeleporterAccident why we're finding Limbo parts scattered throughout the system]].
* Reaching the lowest reputation possible with New Loka makes them suddenly dial the creepy-factor up to eleven if you then visit their syndicate menu.
-->'''New Loka Commander:''' You're just like the rest. Tainted and ruined beyond salvation.
* On the relays, some of the Red Veil are preparing to vivisect a captured Grineer. Also, they have several infested in a cage, for unknown purpose.
* Desert Skates, at least once you see their underside, are pure BodyHorror. Seriously, [[http://img2.wikia.nocookie.net/__cb20130812223114/warframe/images/5/5d/CBskate.png that is not the face of mercy.]] It's easy to think that the average Desert Skate WasOnceAMan...
* The cryptic message you find in the Orokin Derelict at the end of the Stolen Dreams questline.
-->All-All is silent- Hushed-hushed and empty is-is-is the womb of the sky.
-->'''All is silent and calm. Hushed and empty is the womb of the sky.'''
* You have read all of the entries here yes? The Sentients are '''returning'''.
* Grineer Manics. You're just going about a mission,happily killing things until you start hearing this insane laughter and then these things show up. They can be seen as mini-Stalkers, seeing as they can turn invisible and invulnerable,can regen health, can [[NoSell Dispel]] your abilities, and can easily kill you if you're not cautious.
** The Blackout tactical alert. [[NothingIsScarier There are no enemies]] until you reprogram the navigation computer. Then 75 Grineer Manics appear out of nowhere...