Scar plots to kill his family members here. Do we need to explain why that's evil?
SCAR: I'll be king, undisputed, respected, saluted, and seen for the wonder I am.
Scar's power-hungry manipulations mark him as a truly evil and malevolent character.
SCAR: My teeth and ambitions are bared.
Here, we can see how closely ambition—i.e., the desire for power—is linked to violence for Scar.
SCAR: Long live the king.
Scar says these words to Mufasa as he's throwing his brother off the sheer face of a cliff. At this point in the film, it looks as though evil is triumphing over good.
NALA: Everything's destroyed. There's no food. No water. Simba, if you don't do something soon, everyone will starve.
With her deep sense of responsibility and desire to restore good to the Pride Lands, Nala is a perfect interlocutor for the world-weary and insecure Simba. Sadly, it will be a while before the young prince is fully convinced to return home.
NALA: He's gone back … Simba's gone to challenge Scar.
Nala is talking about the final battle between Scar and Simba—the one where the ongoing struggle between good and evil is finally settled.
SCAR: I am the king—I can do whatever I want.
Scar's power-hungry megalomania is beautifully described in this quote. He's in direct opposition to his brother, who only believed in doing what was right for his subjects.
SIMBA: I'm not a murderer!
Simba finally understands that it was Scar who killed Mufasa. This purges him of his guilt and makes it possible for him to defeat his evil uncle.
SIMBA: You don't deserve to live.
Simba says this to Scar after Scar confesses to Mufasa's murder. The young prince is clearly in support of the death penalty for murderers.
SCAR: It's the hyenas who are the real enemy! It was their fault! It was their idea!
A final showcasing of Scar's evil: he shifts the blame whenever he can, trying to save his own hide by blaming the hyenas for his machinations.