She was an alien of extradimensional origin. she is a cruel, cold, and calculating woman who destroyed all life in her own dimension, Charn, before putting a sleep spell upon herself until she was awoken by Digory and taken to Earth, and eventually Narnia upon its creation by Aslan. 900 years later in Narnia, Jadis enacted an endless winter for a century, becoming known as the White Witch. Jadis raised an army in her evil ways that are at odds against Aslan's creation and the four prophesied children who would have a major part in defeating her.
She paid "a terrible price" to learn the Deplorable Word and used it to destroy all life in her entire universe of Charn just cause she couldn't win the war over her sister (who ended up dying by Jadis' actions). She even blamed the destruction on her by claiming that she forced her to do it even though she did so herself by her own doing, meaning that she took no responsibility for it. There are many reasons why this act is not off-page villainy, mainly cause the city in Charn is expounded on greatly:
The walls in the city in Charn were crumbling, and it has been a millennium since Jadis put the sleep spell upon herself. In addition, there are no lifeforms in Charn other than Jadis, no ants, no spiders, not even plants.
In one of the hallways, there were images of Charn's royalty. At the beginning of the hallway, they were friendly rulers, but further, through the hallway, there were worse and worse rulers until it all came to Jadis, after which there were no more people. This indicates that her line of royalty ended with her and she was the sole person to use the Deplorable Word, as the rest of her family kept it a secret.
As soon as she left her universe alongside Digory and Polly, it was reduced into nothing but a blank void, as she destroyed everything that lived in it.
Last but not least, after Digory and Polly go from the world of Narnia to the Wood between the Worlds, Aslan, the creator of Narnia, warns them that it's uncertain that a wicked person will find something as evil as the Deplorable Word and use it to destroy all life, and that nations here on Earth will be ruled by despots who will be just like Jadis when she was a ruler of Charn. This shows that Aslan is fully aware that Jadis used the Deplorable Word to destroy all of Charn's life and uses it to foreshadow the rise of future dictators who would rule over nations from our world.
She demanded that Digory and Polly take her to their world because she desired to take it over as well, going as far as to seize Polly by the top of her hair where it hurt the most.
She threatens Uncle Andrew that if she finds any signs of disobedience in him, then she'll torture him by casting spells on him that anything he sits on will feel like hot metal and that he will feel invisible blocks of ice in his bed.
She attempted to "blast" Aunt Letty (or turn her into dust) as she did with the palace gates of Charn because she wouldn't bow down to her; and when that failed, she threw her across the room.
And since she said that turning people into dust is what happens to people and things that get in her way, this highly implies that she has done this to some of her subjects before.
She caused chaos in London when Uncle Andrew took her out in at least 3 different ways:
By robbing a jewelry store.
Stealing a hansom cab and whispering stuff in the horses ear to make it be a hazard to be around.
Tearing off the lamppost rod and using it as a weapon.
She assaulted or threatened people at least 3 times with the iron bar she tore off the lamp post:
She assaulted 2 policemen by ramming it on their helmets, and would have done more if Digory hadn't interfered and sent her to the Wood Between the Worlds.
She threatened to ram the iron bar at someone's head if they came within 2 paces of Digory and Polly for the rings.
She assaulted Aslan by throwing it at his head between his eyes, although it did no good.
She ate of the fruit that would eventually corrupt her; and tried to tempt Digory to do the same. And after he said he didn't want to, she tried to tempt him to take one to his mother, and possibly might have succeeded if she hadn't suggested leaving Polly behind.
She led more lives to follow in her footsteps for many millennia.
She tortures and murders Aslan's followers.
She turns Mr. Tumnus into stone when he refuses to bring Lucy Pevensie to her so she can kill her.
She corrupts Edmund Pevensie in an attempt to kill him and his siblings to keep the prophecy of her defeat from coming true.
Kidnapped Edmund and sent Maugrim to kill his siblings, as well as Mr. and Mrs. Beaver.
She turns an innocent fox and his friends into stone because over the gifts they received from Father Christmas out of pure hatred for him and the holiday. She also dismisses them as insignificant trinkets compared to her own “gifts” based on her display.
In the 2005 film adaption, she turns only a fox to stone for betraying her to save the Pevensies.
She murders Aslan in a painful and humiliating ritual. Though their deal was for Aslan to die in Edmund's place, Jadis spitefully reveals to him that she was going to have Edmund killed anyway, and mocks him about losing his own life and not saving Edmund's.
Rages a war against Aslan's troops, turning several of them into stone. Edmund is also fatally wounded in the process.
In the BBC series and 2005 film adaption, she stabs Edmund herself for destroying her wand.
In the film adaption of Prince Caspian, she nearly succeeds in corrupting Peter to her side upon almost being resurrected.
✓
Pure Evils
