Special mention goes to Scar screaming "YOU WON'T GET A SNIFF WITHOUT ME!!!" at one of the hyenas, who promptly falls screaming into a pit of what we can assume is boiling lava. That's right, the hyena he yelled at dies.
The scene of Scar leaping at Simba, teeth 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.
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.
And Mufasa's death.
The Wildebeest Stampede. Oh GOD!Poor Simba! We know the the Hyenas started the stampede, but in Simba's perspective he thought he was the one who caused the action that led to his father's death.
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.
When the stampede starts and the thrill chords start, we get a good long look at Simba's utterly terrified face.
Scar manipulating Simba into thinking it's his fault Mufasa died while they're standing near Mufasa's dead body and then when Simba runs away Scar orders the hyenas to 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 hitting on Nala, wanting to her to be his queen, but she refuses. 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.