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Nightmare Fuel: The Land Before Time
First he'll kill your mother, then come after you.
The tar pits. Seeing all the innocent, rather young protagonists getting submerged in black gunk and nearly losing their lives is not a fun thing to watch at the age of 6 or in your adulthood. The 'tar monster' that the characters form to scare Cera is also pretty morbid in appearance, and definitely isn't pretty to look at, either. It looks like some sort of Eldritch Abomination, honestly. Made worse by the horrifying noise made by the "tar monster".
Sharptooth himself IS this trope. Imagine a large,extremely vicious T-Rex that simply does not give up until he kills his target, no matter how many times said target escapes. Not to mention the fact that he is extremely feared by the main charaters (can you blame them?!)and they have to live in constant fear of him. The scene where the beast ambushes them while THEY WERE ASLEEP shows that he can attack ANYWHERE.
You think he's bad in the movie? He's even worse in the novel. In the movie, he's mostly portrayed as an instinctive force of nature, but in the novel he's almost portrayed as a narcissistic serial killer who fancy himself above other dinosaurs. And the novel confirms he's deliberately hunting the children for no reason but for petty revenge, and during his hunt, he toys with them just to enjoy seeing their terror before he kills them. And when he finds the entrance to the Great Valley, the novel says that he growled and sniffed the air "in evil joy", which would hint that he really mostly kills other dinosaurs just For the Evulz, and the next thing he plans to do after he kills the childen would be going aroung doing a killing spree in the Great Valley.
The Eye Awaken moment just before Cera can use the Sharptooth's head as head-butting practice.
The many instances where the characters almost died horrific deaths. They're supposed to be really small children, even if their ages are somewhat vague.
The Swimming Sharptooth in The Journey to Big Water. Its eyes are pure yellow, and its face looks vaguely like a crocodile's skull. The worst part is that it is in the water. You won't be able to see it or hear it until it attacks, and if you're in the water, you are helpless against it.
It doesn't help that it's a Expy of the Liopleurodon from BBC's Walking with Dinosaurs, and that it boasts probably the most accurate design of any of the Land Before Time creatures
The Giganotosaurus from the fifth movie has one of the most intimidating designs to date, and it friggin' tosses around other Sharpteeth. It's also the only character to shed blood in the entire franchise.
The scene in the first film when a newborn Ducky jumps directly into the mouth of a giant snapping turtle. Thankfully, her mother manages to grab her in time, but there's some major Adult Fear right there.
It does manage to show how courageous and curious Ducky is, though.
Rinkus and Sierra from "Stone of Cold Fire". Rinkus starts out seeming like a comically ineffectual villain, but shows his true colors later on in the film as a disturbingly realistic sociopath. Sierra, on the other hand, is easy to summarize; violent, hateful, sadistic and all too willing to kill a group of small children. Rinkus, meanwhile, starts out seeming like a silly, Dirty Coward (being voiced byPinky undoubtedly helps in that regard), but then we find out just how nasty he truly is when he plots with Sierra to use Pterano to both their advantage and, in his words, "let him lead [them] to the stone". And when Pterano proves himself to be entirely useless to them, Rinkus drops his loopy, cowardly persona, implying that said persona was fake all along...