The Red Alert 1's portrayal of Soviets in general and Joseph Stalin in particular. The very first thing you see in the Soviet campaign is the aftermath of a Sarin gas test, with Stalin and his attaches going over the results. The first mission they give you involves burning a Polish village to the ground and killing everyone and everything inside. It only gets worse from there.
Another example of his unpredictable nature comes about during the mission he instructs you to capture the Chronosphere. When you do finally capture it, there is a cutscene showing it going unstable and then exploding. Cue Stalin angrily ordering that you be be executed, until the secretary informs him that one of the other officers gave you incomplete/faulty intel, whereupon he personally strangles the man.
During the Allied campaign, there is a tense series of missions whereupon you are tasked to rescue an officer who wished to defect from Stalin's regime, whereupon he confirms Stalin's plan to launch nukes at the Allies. It's the desperation in which he begs you to stop his former Premier that will unsettle you.
The worst part of the portrayals are when you realize that, unlike Red Alert 2 and 3, these were rather accurate and, more importantly, realistic. Stalin, in particular, proves to be a very accurate portrayal of one of the most frightening dictators in history. Also see Shown Their Work below.
The Chronosphere technology proposed by Einstein in this series has a horrifying side effect that is only seen in the first Red Alert: Every so often, the abuse of Chrono technology will cause a Chrono Vortex to form. An enigmatic swirling distortion in the fabric of reality itself, the Vortex will tear apart any troops, vehicles, and buildings that happen to be in its path as it meanders around the map. This unstable Chrono Technology also exhibits the side effect of killing all passengers inside any APC transports when you teleport them, in a parallel to the mysterious deaths attributed to the urban legends of the Philadelphia Experiment that were the inspiration for the Chronosphere.
Later "stable" versions of the Chronosphere seen in Red Alert 2 have an offensive bent that will terrify enemy commanders: Besides allowing a canny commander to teleport vehicles around, you can also use the Chronosphere to pick up enemy vehicles and send them wherever you please - it is entirely possible to drown tanks and shatter ships upon dry land with this technology wielded as a weapon. Furthermore, the effect of the 'stable' Chronosphere is deadly to infantry not in the safety of a vehicle.
Modified versions of Chrono technology as wielded by Chrono Legionnaires and the IFV with a Legionnaire passenger allow them to invoke the power of Retgone upon enemies, erasing them from time in the same fashion as how Einstein accidentally started the Red Alert timeline in his all-too-successful attempt to eliminate Hitler. The Paranoia Fuel invoked by a white-armored teleporting figure who erases things from existence could potentially cause some real freakouts.
One of the penultimate Soviet missions in the Counterstrike expansion, Paradox Equation, has you being assigned to capture a Chronosphere in a region badly warped by the effects of experimentation with it. How badly are we talking here? Try having every unit's weapons being altered into something completely different, like tanks with Tesla and Flame cannons, Artillery pieces firing oversized rounds, and V2 launchers suddenly finding their payloads boosted to near-nuclear levels. The mission briefing itself adds to the surreal horror:
TO: Field Commander S7 FROM: Soviet Command PRIORITY ONE We received this garbled transmission from a scout group sent into a suspected Allied test site: <TRANSMISSION BEGINS> All... te.t area di..overed! Chronos... test g... crazy! Weapons... effected by... air units inop... Area unst.able! Ch...osphere must be affect... <TRANSMISSION LOST> You are to investigate this. If the Chronosphere is indeed behind it, this is a perfect opportunity to capture it. See that it happens.
- Mission briefing
Red Alert 2
Yuri's Mind Control is rather frightening, considering the tactics of mind controlling enemies, civilians and what else to send them into a grinder or to increase power to your bio-reactors. Could cross into And I Must Scream when you think if they're completely aware of being mind controlled before being turned into a Living Battery or ground up for spare cash.
The intro of Red Alert 2, which is unskippable for the first-time run, has him brainwashing one of the American missile control staff, turning him into a blank stare while aiming a gun to his friend to threaten to self-destruct American's nuclear arsenal. The worst part is that you don't even need to be in his presence; a phone call is all he needs to mind control you.
A lot of Yuri's ideas for units are downright cruel and unusual along with exploding into a virus cloud, going berserk and killing your allies, being mind controlled, having your vehicle pulled to your imminent doom/mind enslavement, irreversible mutation into a muscular brute or just outright being enslaved to dig up ore and gems from the ground until hopefully some capitalist/communist comes along and destroys the miner you're enslaved to.
Yuri in RA2. He's not as scary as Stalin, he's still a huge Knight of Cerebus amongst amongst a bunch silly villains. He's extremely stoic, controls people's minds, and his voice alone just screams "this guy is evil, don't trust him you idiot." Of course, by the time you heard his voice, trusting and obeying him is no longer up to you... Probably the worst in the RA2 vanilla soviet ending is when we see him with his calm attitude when reduced to a Brain in a Jar. His faction has some of this with his Grinders, they break stuff down into material components...Including people.
One of his threats in the "Brain Wash" mission of Yuri's Revenge is particularly chilling. Knowing who Yuri is and what he can do, it's not an idle one.
General Vladimir, in the Allied mission "Last Chance", addresses the player with a chilling speech as he destroys Chicago.
"Hear me, you foul American phantom, wherever you are. You can work your armies like a puppeteer all you want, but this is my play! Here is the city that you have saved, without the Psychic Amplifier, which you so rashly destroyed, I no longer have much use for it. Behold. The power. OF MOTHER RUSSIA!!!"
Terror Drones are actually dismantling the vehicles, the crew just dies from the resulting explosion (that's why you have to repair them to get the drones off). However, note that the Drones were designed with Dismantling Vehicles in mind and was only suppose to do that. The butchering of infantry was when the Soviets realised the same tools used to cut through metal and sever cables can be used to do the same to human flesh and limb.
Attack dogs and war bears. Imagine trying to fire your weapon like crazy at them before they lunge for your neck.
Soviet Desolators would be a horror to face in battle. No soldier is safe from the lethal radiation beam cannons they wield, and the Red Alert 2 incarnations of these deathbringers can slam their cannons into the ground and make a large patch of land so toxic infantry die rapidly. Their sadism and the sickly-green glow makes them seem even more inhuman.
Red Alert 3
Yuriko Omega, she's a Person of Mass Destruction whose dialogue points to her not being completely mentally stable. It was recorded that amongst her personal kill-counts includes an entire Allied company including a mix of infantry, vehicles, attack helicopters, ships, and a school of Allied-trained recon dolphins.
One of the reasons for there being multiple Yuriko operatives in the Imperial Army's forces is that the original was held in Shiro Sanitarium, where other female psychics were transformed into virtual copies of her via horrific treatments. Clones of her were also produced, as recon images of the Psionic Decimator reveal that Yuriko clones are stuffed in its pods.
After the main campaigns of the RA 3 story comes Yuriko's personal quest, Uprising. At the end of the main campaigns, the original Yuriko is taken prisoner by the Allied forces until she receives a telepathic message from her sister, who was also held in the Shiro facility, which engages in a variety of dehumanizing and brutal procedures to produce and train psychic commandos like Yuriko herself and her clones. She escapes from the Allies, and fights her way back through the facility, where she does succeed in freeing her sister. However, they have a falling-out, and Yuriko is forced to kill her sister in self-defense. About the only thing good that happens of this incident is that Yuriko destroys the facility that made her into a mentally-unstable psychic commando, preventing more clones of herself (and more psychic commandos) from being produced.
The effects of the freeze beam and shrink beam. Imagine getting frozen alive, and can only watch in horror as a man with a shotgun comes up to finish you off. Or imagine you're in an apocalypse tank, crushing Capitalist pig-dogs, when all of a sudden you're shrunk to the size of a kitten, and see guardian tanks coming up relentlessly as your shells ping off their armor harmlessly.