The scene of Scar leaping at Simba [shown above], teeth and ambitions bared and claws out with fire burning behind him. He looks like Satan leaping out of Hell. Try seeing that in 3D.
The leadup to it. After Scar has tried to kill Simba and fallen into a crevasse, Shenzi, Banzai, and Ed approach. Scar addresses his friends, to which Shenzi says, "Friends?" I thought he said we were the enemy?" Shenzi and Banzai turn to Ed... who breaks into a creepy giggle like nothing we have heard before... and it is both TERRIFYING and AWESOME.
It also implies - as confirmed by Jim Cummings about Ed faking his craziness - that Shenzi and Banzai know Ed is dangerous and know that if he decides that Scar is fucked, then Scar is fucked. It could probably be why Scar figuratively shits himself at the laugh.
Notice also that Ed is, throughout almost the entire movie, laughing or scared with unfocused eyes. When they first approach Scar at the end, his face is pure rage and he is staring straight at Scar.
Following that, we see Scar begging for his life as he is surrounded by a gang of looming Slasher Smiles, followed by a quick Shadow Discretion Shot as they pounce and tear him apart—
Scar: (Relieved) Ah, my friends.
Shenzi: "Friends?" I thought he said we were the enemy.
An early draft of this scene has Scar saying, "My friends," when the pack of hyenas approach instead of Shenzi, Banzai, and Ed approaching first and the trio aren't even present. In fact the script implies that Banzai and Ed die when they are catapulted into a flaming tree; Shenzi is the only one who approaches from behind and hears Scar betraying the hyenas; she disappears after this. The final scene is enacted with no dialogue from the hyenas, they just erupt in a "choir" of eerie laughter as Scar slowly realises he's screwed.
The stage version of Scar's death changes it to where Scar is injured by his fall from Pride Rock, and is unable to get up, and asks his "friends" for help. The dialogue occurs, but Ed is perhaps even more terrifying than his animated counterpart, because when asked, he breaks out into extremely deranged, cruel laughter, and then shrieks as he leads his comrades into eating Scar. What's worse is that we barely get a Shadow Discretion Shot; the curtains come down, and we see the silhouettes of the hyenas eating Scar alive while he screams, their heads going up and down as they tear into him. Sweet dreams.
And Mufasa's death.
The Wildebeest stampede.
The film uses a discretion shot for Mufasa's death (he disappears in the dust as he falls, and we only see his body after the fact). In the companion book The Art of The Lion King, there's a piece of concept art that actually shows Mufasa getting trampled. Every bit as horrific as it sounds.
Don't forget his helpless scream as he falls to his death...replaced with the scream of Simba as he watches his dad, who he just had a scene showing their closeness, fall to his death...
Scar's behavior as well. At first, when Mufasa is calling for help, Scar seems to ponder what to do, as if he's realized that there would be no turning back if he killed his brother... and then not only he does it anyway, but takes some moments to enjoy Mufasa's terror. This isn't useful to his plan but highlights his sadistic nature.
When the stampede starts and the thrill chords start, we get a good long look at Simba's utterly terrified face. Provides the page image for Oh, Crap!.
Scar manipulating Simba into thinking it's his fault Mufasa died while they're standing near Mufasa's dead body.
Scar's order to the hyenas as they emerge from the fog after Simba runs off is chilling in its brutal simplicity. Especially since he doesn't even look in their direction as he gives them the order.
Scar: Kill him.
A deleted scene that is mostly restored in the play as "The Madness of King Scar" is downright creepy. The play version is simply discomforting. The film version is downright disturbing. Scar starts to show feelings for Nala, wanting to her to be his queen, but she refuses his advances. In front of the entire pride, he banishes her. In and of itself the scene is mildly unsettling. The way Scar says his lines, though, is outright disturbing.
From said animated version, we have what happens when Nala claws Scar to get him away from her. He looks shocked, then sneers and says "Ahh...Nalaaa..." Just...the way he says it coupled with the look on his face will probably make you feel extremely unclean...
The hyenas' laughter as they enter Pride Rock when Scar names himself king.
"Oh, Simba, you're in trouble again. But this time Daddy isn't here to save you... and now EVERYONE KNOWS WHY!!"
When Zazu has been captured by the Hyenas, who like to play with their food...two words: "Birdie Boiler". It's a Played for Laughs scene, but to anyone who's ever been bullied, it can come across as pretty unnerving.
Not to mention the way he says "Oh, no, not the birdie boiler!" hints that it may not be the first time.
The Pridelands under Scar's regime. What was once a lush savannah paradise is transformed into a parched, desolate wasteland. Littered with countless animal skeletons, dead trees, and infested with ravenous hyenas, one has to wonder how anyone managed to survive for so long.
The part where Scar strikes Simba's mother Sarabi when she mentions Mufasa was particularly unsettling.
Sarabi: We have no choice, Scar. We must leave Pride Rock. Scar: We're not going anywhere! Sarabi: Then you have sentenced us to death. Scar:Then so be it! Sarabi: (understandably disgusted) You can't do that! Scar: I'm the king! I can do whatever I want! Sarabi: If you were half the king Mufasa was— Scar: (smacks Sarabi and knocks her unconscious) I am TEN TIMES the king Mufasa was!!!
The three hyenas are a source comedic relief for the film, but during the climax, they don't appear much, instead focusing on the rest of the clan, who prove they truly can be a force to be reckoned with, as an entire pack of them dogpiles Simba and attacks him rather brutally after he makes Scar reveal the truth, even when the lionesses join the battle, you can see the hyena army fighting back viciously as well. And the whole time, they don't laugh, but utter primal growls, snarls and howls of sheer fury. Thankfully, the combined strength of the lionesses helps drive the unnamed hyenas away... just in time for what they have in store for Scar...
Right at the start of the battle, while Simba tosses a few hyenas around, one gets the jump on him and goes for his throat. If it weren't for Rafiki showing up at that moment, it's possible that hyena would've torn Simba's throat out.
It's a brief moment, but during the shot where some of the hyenas are running away, we can see a male lion and a lioness shoving and knocking hyenas into the fire. That is right: Simba and Nala knocked several hyenas off a cliff and presumably killing them. Beware the Nice Ones, indeed. Also shows how serious this film is, since this is the first time that we see a Disney animated hero killing someone aside from the main villain intentionally.
During the Elephant Graveyard chase, Shenzi comes perilously close to chomping down on Nala, before her cheek is slashed by Simba. It actually draws blood, and Shenzi freezes in pain... before slowly turning to Simba with a completely furious, but subdued growl, Simba having genuinely angered her.
In the stage version at the end of "Chow Down", the cubs are trying to climb away from the hyenas up the elephant skeleton piece, but the hyenas succeed in dragging down Nala. They lick their chops and cry out "Yum yum yum!" and what not, and we see all three hyenas lunging to bite into Nala before Simba stops them in their tracks with his pitiful roar.
At the end of the Broadway version's trailer on the "The Lion King II: Simba's Pride" 1998 VHS, there is a black outlined drawing of Simba that is sure to give kids nightmares (Trust me, it almost gave ME nightmares when I was a kid!). It also doesn't help that there is a male announcer shouting, "WINNER OF SIX 1998 TONY AWARDS, INCLUDING BEST NEW MUSICAL: "THE LION KING"! VISIT DISNEY.COM FOR MORE INFORMATION!" The first part of the trailer does a really good job of persuading you to see the musical, but the ending is scary as hell and comes out of left field! The musical was great, but the scary end of the trailer doesn't do it justice. What's weird is that the drawing of Simba is nightmarish here, but not in the first movie. Maybe it's the curvy eyes that don't look like eyes at all, or again, the black outline, and the INCREDIBLY LOUD announcer.