Jafar. While he did have a bit of a temper in the original film, he balances it out with his slick charm. Here, he's like a volcano that is ready to blow at any minute.
The film wastes no time in establishing just what kind of a man he is, forcing a clearly reluctant man into The Cave Of Wonders at swordpoint. The camera then pans to make it seem like the "eyes", are glaring right into your own, only for the jaws to snap down and cut off a terrified scream...
Jafar tops himself a few scenes later when a loyal but clueless guard keeps pressing his Berserk Button. The hapless fool is thrown down a deep oubliette with a scream of despair where he likely perished.
Whenever Jafar hypnotizes someone with his staff. The victim's eye color changes and Jafar's voice sounds a lot deeper. At one point, he tries to hypnotize Aladdin disguised as Prince Ali to ally with him. Luckily for Aladdin, Genie intervenes.
When Jafar uses his second wish to become a sorcerer, he demonstrates his power by conjuring a real cobra and turing it into a new staff. It even hisses and spits in a few scenes!
When Jasmine steals the lamp from Jafar, it appears to be a suicide attempt, and the horror on the Sultan's face is awful to see. Also doubles as a brief Tear Jerker.
Jafar transforms Iago into a giant demonic rukh after Jasmine steals back the lamp from him and escapes with Aladdin on Carpet. While brief, Iago is unleashed on a deadly rampage after the heroes, with them only escaping by the skin of their teeth.
Jafar as a genie has a few moments of fear right before being bound by the magical conscription of his new form. His first act with all that phenomenal cosmic power is to blast away Shirabad all the way from Agrabah.