This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Treasure Planet
As soon as you see Scroop with the rest of the crew, you just KNOW he's the one you really do not want to be alone with.
While we're on the subject of Scroop, on the ship when Jim steps out to shoot at Scroop, the lights suddenly go out, courtesy of B.E.N., who is trying to disable the laser cannons, and the emergency lights turn on, revealing Scroop has disappeared. As Jim looks around, Scroop appears above him about to strike.
The way he walks resembles a spider, which is not good news to anybody who suffers from arachnophobia.
In a subtler way, the revelation that Silver is planning treachery (along with either murder or a mass marooning) makes his pleasant behavior quite chilling.
The confrontation between Jim and Silver after Jim overhears the mutiny. As they're both speaking, Silver turns his mechanical arm into a pistol behind his back, apparently intending to shoot Jim.
However given how he stopped from shooting Jim when he (along with Captain Amelia and Doppler) were about to escape, it's likely he was just going to scare Jim and/or take him as a prisoner.
It's not easy to see at first glance, but pay attention to Silver's face in the background when Jim is reaching for the knife; he has a sad expression as he prepares to point the gun at him.
Which becomes horrifyingly averted during the destruction of the planet when they confront each other on a ship loaded with gold when he admits to Jim, who is holding a cutlass out to defend himself, that he likes him, but that he's come too far to let Jim stand between him and the treasure. Then he begins moving menacingly toward Jim, who is backed against the helm. Thankfully, they're interrupted by a laser beam knocking them off the ship.
It can also be rather creepy how, when Silver realizes Jim heard them, he instantly switches from the benevolent father figure he'd been the night before to an intimidating pirate captain, backing Jim into the room as he asks him with a threatening voice if he's "playing games".
When Scroop is sent flying into space. At first, it seems like no big deal, until you realize he's trapped in space until he dies of dehydration. The look of terror on his face makes it worse.
But then again, he was responsible for Mr. Arrow's death.So fuck him.
Mr. Arrow's death scene.
Hell, what about the goddamn BLACK HOLE?! That entire scene was terrifying!
Look. At. His. Face.
The fact that Jim was so close to falling and could have died a horrible death of being burned alive by the planet's core.
And the audience is previously treated to scenes of some pirates who weren't so lucky and suffered that exact fate.
It's a Freeze-Frame Bonus, but when Silver grows impatient and starts zapping through the map one of the worlds he lands on houses this giant, centipede-like... THING that looks less than amiable. It lunges towards the crew with a gaping maw, and was so close to reaching the portal had Silver not quickly switched.
THE. BLACK. HOLE. Enough said. See the page image as to why it's so terrifying.