Vexen is number IV in Organization XIII he weights a spiked shield and control the element Ice.
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Vexen was on the same mission and working under Marluxia. But he was used then betrayed.
History:
[SPOILER - highlight to read]: Vexen sides with Zexion and Lexaeus, other high-ranked members occupying the castle's basements, to prevent Marluxia, whom Vexen dislikes, from using Sora to overthrow the Organization. He first battles Riku in order to gather data to create a replica of him. However, Vexen cares nothing for his "experiment" and allows Naminé to manipulate the Riku Replica's memories against his wishes. When the Replica fails to defeat Sora, Marluxia threatens to reveal the shortcoming to Xemnas, forcing Vexen to kill Sora. Encountering Sora, Vexen says that he came to collect his "debt" and provokes Sora's anger by making him believe that he controlled Riku rather than created a replica. After their battle, Vexen gives Sora the card to Twilight Town with the intention of revealing Roxas's existence. Marluxia considers him a traitor as a result and sends Axel to kill him.
In Twilight Town, Vexen attempts to reveal to Sora why he feels as though he has been to Twilight Town despite being fairly certain that he had never been there. Sora and Vexen battle again after Vexen tells Sora to throw away his memories and listen to his heart. After being defeated, Vexen sees Sora as a true threat; even after being weakened by false memories, Sora remained very strong. As Vexen is about to reveal Marluxia's plot, he is killed by Axel.
Powers Abilities
Vexen uses a Shield which can block any frontal attack made on him. He is able to call spikey icicles from the floor either to attack enemies or defend himself or make them rain from the sky. He is able to freeze a person where they stand, then strike them with the spikes on his shield. He may also launch a fast Icicle that tracks the target