Megatron. Giant, genocidal lunatic made of jagged alien metal with a booming, snarling voice. Can't be stopped or slowed down by normal means. Ripped Jazz in half with his bare hands like it was nothing. CGI just a little too realistic, there... Megs looks entirely too much like they actually had a giant alien war machine in front of the camera.
Speaking of Megatron, the "I smell you, boy!" line that he said when chasing Sam up the abandoned warehouse was quite creepy.
Megatron's mutilated face in DOTM. Not to mention that he has several Scalpel-esque robots crawling around in his giant gash.
The death of Ironhide. Here's what happens. Right after the Highway Chase scene and the Mexican Standoff scene, Sentinel reveals his role as the Big Bad of the film and shoots Ironhide two-three times. You'd think that would be the end of it. But no, you witness Ironhide rusting up and dissolving to the point where his head falls off his shoulders and the rest of his body just sags apart. It's such an emotional punch and to hear Ironhide groaning and letting out his last breath is nightmare inducing.
It's also horrifying because it happens completely out of the blue. It is completely unexpected.
The Decepticon's apocalyptic takeover of Chicago. Complete with genocide and screaming survivors. And people getting vaporized onscreen! A skull fell after one person was shot.
Laserbeak, full stop. He could be anywhere, pretending to be anything, not to mention the fact that he's a merciless, coldblooded killer.During the film, Laserbeak takes on a series of insidious disguises, including a printer, a flat-screen television and a computer monitor. However, that quote comes from when he turns into a pink Bumbelbee-esque robot and befriends a little girl to kill her father.
"Is your daddy home?"
Shockwave's "pet", The Driller. Imagine a mechanical worm that's bigger than Devastator, with a mouth made of a series of buzzsaws and grinders, and able to dig and hide underground and unleash terrifying destruction.
It also becomes a bit of Fridge Horror when you learn that it's actually a domesticated Cybertronian beast (similar to Laserbeak, Ravage, and the Insecticons). Meaning that at one point there were hundreds of them burrowing through Cybertron.
Remember that car your girlfriend's boss gave her? That $300,000 car. It's a Decepticon, specifically Soundwave, and he's just kidnapped your girlfriend, threatening her with his tentacles.
Alice... Just Alice... She is a Decepticon in disguise sent to kill Sam. She looks and acts just like a normal human girl so you would have no idea who she really is until it's too late. Her appearance doesn't help... Also, LOOK AT HER FREAKING TONGUE!!!
On the subject of Alice, what the hell was she going to do to Sam when she went on top of him in Leo's dorm room? Was she going to force him into having sex with her and kill him during it or just kill him?
Just the fact that there are Transformers out there than can transform into humans are terrifying if they're Decepticons. Just the thought that not only could vehicles be machines, but humans as well. . .
There's a brief scene in ROTF when Scalpel and a team of Decepticons are going to revive Megatron from his watery slumber but in order to do so, they need to repair his missing parts. So what do they do? They proceed to tear one of their teammates apart just so Scalpel can fix Megatron. Granted, the Decepticon does seem to survive the attack since the submarine sonar does pick up 6 "hostiles" instead of just 5 like there would be if the Decepticon had been killed, but still... the way they were just tearing him apart and his muffled screams of pain and terror are just... *shudder*
"No prisoners... Only trophies..."
That blue energon in the first movie that's supposed to be Symbolic Blood...In ROTF and DOTM, it's been replaced with red energon. Seeing giant gobs of blood-colored energon flying at you whenever an Autobot or Decepticon got ripped apart...
"Laserbeak, kill them all."
Starscream's death. Just imagine all the pain he went through. First one eye is ripped out and then another has an explosive device stabbed into it. He spends his last seconds screaming while blind before having his head blown in two.
You wouldn't want to listen to the track "Cybertron" from the first movie alone in the dark. 0:51 is where the really chilling stuff starts.
From the original comics in the 80's comes the Smelting Pit. A place where Decepticons toss captured Autobots, and they melt and desolve to death slowly over several days. Made worse as we see Scrounge, a charecter we'd gotten to know in the previous issue reduced to a torso, then melt to nothingness, while his friend Blaster tried to save him.