Game:Vexen

Kingdom Hearts: Chain of Memories
An easy way to defeat Vexen is by using sleights in high succession. Blitz and Sonic Blade are powerful and do large amounts of damage. The Jafar card is very good to use in this fight, as it will prevent Vexen from breaking your attack cards. Make sure you also leave three or four zero cards at the front of your deck in order to break his sleights, Freeze and Ice Needles. Put some Cure cards at the back of your deck as well to be used in combonation.

As for avoiding Vexen, keep moving. When Vexen says, "I'll freeze you!," start dodge rolling so he doesn't catch you in his ice block. When he slams into the ground, keep running to avoid the ice spikes that will follow you around the battlefield.

This battle can be very difficult, so just keep trying. The Jafar card can save you, however, as it will prevent Vexen from his annoying habit of breaking your sleights with zero cards.

Kingdom Hearts II: Final Mix+
Vexen appears as an Absent Silhouette and a Data Battle.

In this battle, Vexen wields his shield in front of him, preventing you from damaging him until you deplete its HP bar. Vexen commonly throws spinning shields at you, you may get rid of them by guarding or reflecting. He will also throw up pillars of ice, and is easily avoided by dodge rolling. At times, when you suddenly see snowflakes reflecting across the screen, use reflect, so you don't become frozen and have to break out.

Vexen also has a data circle that follows Sora around, do your best to avoid it. When it gets to one, Vexen summons an Anti-Form Sora, and can be troublesome. It then can go to 2, 3, 4, and 5, each time making a more powerful Anti-Form. If your magic is high, use Reflect, and you would be able to kill it quickly.

Vexen's weakness is Fire. After you get his shield down, go into Final Form or Wisdom Form and spam fire. It would be useful to use the keyblade Bond of Flame to damage him quicker. When he summons his shield again, rinse and repeat.