Vexen is fought as a boss in Kingdom Hearts: Chain of Memories, Kingdom Hearts Re:Chain of Memories, and Kingdom Hearts II Final Mix. First appearing to Riku in hopes of recruiting him to help accomplish his goals, Vexen instead was defeated and obtained valuable combat data he would later use to test Riku and even Sora in the form of the Riku Replica. His "product of pure research" dubbed a failure by Marluxia, Vexen later appeared before Sora to prove himself and his strength to his traitorous fellow Nobody. He then craftily lured Sora to the memory-based Twilight Town for a second battle, hoping to ruin the rebellious Marluxia, Axel, and Larxene's plans to take over the Organization at the same time. This attempt led to Vexen's own elimination, however, at Axel's hand, the Nobody appearing to Sora a year after these events transpired as both an Absent Silhouette and a Replica Data.
Strategies
Kingdom Hearts: Chain of Memories
First battle
At the beginning of the battle, the player should immediately begin to attack Vexen, but one must also take note of the fact that the boss will Guard against all frontal attacks. Thus, he must be hit from behind. One also should be careful not to abuse sleights, as this will rapidly deplete the number of usable cards in Sora's deck, possibly making Vexen's attacks harder or nearly impossible to Card Break. Any friend cards should be saved for usage in sleights or singular usage if they are of high value, should this occur. In terms of what enemy card to bring into the battle, the player might wish to consider the Oogie Boogie, Captain Hook, Jafar, or Maleficent cards. Each of these will either make attacking Vexen easier or aid Sora in terms of HP and survival.
Should Vexen activate an attack card, he will perform a single slash with his Frozen Pride. This can be dodged with a simple run or even Dodge Roll. If Vexen plays a magic card, he'll shoot a Blizzara spell at Sora. This attack is easily dodged, especially with Dodge Roll. Vexen will also only have access to one sleight, Freeze. When this sleight is executed, the boss will attempt to freeze Sora in a block of ice, damage slowly being dealt to Sora as he's trapped. A well-timed run or Dodge Roll can be used to avoid the ice block, but should Sora get captured, the player will have to wait for the ice to break. Vexen will repeat these tactics throughout the battle, so the same strategies can be used each time. Attack Vexen from behind enough times or bombard him with magic sleights, and he'll fall rather quickly.
Second battle
During the second battle with Vexen, the gloves are off. While his HP remains the same, the boss now has new sleights to use against Sora. The Blizzara and slash attack will return, as well as the Freeze sleight. The same strategies can be used to avoid them. The same enemy cards used to help Sora win the first battle with Vexen most likely will be useful in this battle, as well.
The first of Vexen's new sleights is Ice Burn. This sleight, when utilized, causes the boss to create pools of slippery ice on random areas of the battlefield. When Sora steps on them, his speed will be reduced, and he will merely trip. Careful maneuvering can be used to avoid the ice pools. Vexen also may use Ice Needles, a sleight that causes icicles to rise from the ground as they follow Sora. These icicles will not stop until they hit or until the Sleight runs its course, so it is best the player keep at a constant run to avoid the icicles. Aside from these two new sleights, the second battle with Vexen will be fairly straight forward. His most annoying trick, however, is the reviving ability granted by his Vexen enemy card. While this will increase the length of the battle, this unique enemy card shall be the prize for Vexen's defeat. This can be avoided by using the Parasite Cage enemy card.
Reverse/Rebirth
The battle against Vexen in Reverse/Rebirth mode will be nearly identical to the boss's second battle with Sora in every aspect. The only differences will be Riku's greater power and speed overall, the presence of HP-restoring King Mickey friend cards, and the deadly sleights allowed because of Dark Mode. Vexen lastly has access to a new sleight, Diamond Dust. During this sleight's execution, Vexen will create an ice storm that covers the entire battlefield. Simply Card Break him to avoid the attack. While Riku's movements and abilities are slightly different than Sora's, the strategies for obtaining victory are the same. Simply wait for Riku to enter Dark Mode and use its powerful attacks and sleights whenever possible. King Mickey cards will restore a great deal of HP, so this should be of no concern during the battle to the player. If one is patient and careful, Vexen will fall.
Kingdom Hearts Re:Chain of Memories
First battle
In comparison to the other bosses Sora has faced thus far, Vexen will be the most difficult to overcome. He has a great amount of HP, and the fact that he blocks all frontal attacks can make landing a perfect combo a difficult task. He also absorbs all Blizzard-attributed attacks, so it is important that the player not bring any Blizzard cards into the battle. As he has a one fourth chance of casting Blizzard, the player may wish to save all Donald friend cards for use in a Wild Crush sleight. Vexen has a strong vulnerability to Fire-attributed attacks, so be sure to equip Sora with a deck that will allow the usage of Fire-based abilities such as Firaga, Firaga Burst, and Mega Flare. Bring a couple high-valued item cards into the battle to restore all used cards to Sora's deck, as well as a few Cure cards for the possible Curaga sleight, and Sora should proceed through the battle with flying colors. The player lastly may wish to consider bringing the Red Nocturne (if one wishes to approach Vexen with a Fire-based deck), Jafar, Oogie Boogie, Maleficent, or Captain Hook enemy cards into the battle, as well.
In terms of the battle itself, the player should follow a hit-and-run strategy. Vexen may attempt a slashing combo that ends when he causes an icicle to rise from the ground below Sora, but this can be easily dodged with Dodge Roll. One also can Card Break the attack, causing Vexen to lower his Shield, this not only opening him up to more damage but also being one of the only instances where he can be hit from the front. Show Vexen no mercy when he is either reloading his deck, in a non-offensive setting, or after he is Card Broken. Otherwise, it is best to keep Sora on the move. Vexen may attempt to shoot a homing shard of ice at Sora when he activates a magic card, but Dodge Roll, if one has careful timing, again can be used to avoid this attack. The boss will only have access to two sleights during the battle, as well, both of these easily avoided. The first of Vexen's sleights being Freeze, he will attempt to encase Sora in a block of ice so he can rush forward for a slash attack. Dodge Roll or a Card Break is the best way to prevent to attack. Vexen's Ice Needles sleight, however, is a bit trickier to avoid. While one can Card Break the sleight, if one finds that Sora is out of zero cards or doesn't have a sleight with a higher value, he can either Dodge Roll or keep at a simple run as the icicles follow him around. The sleight will either end once it's run its course or after it hits Sora.
The battle against Vexen should not be that much of a challenge. So long as one doesn't abuse sleights, isn't reckless, and brings a reliable deck into the battle, Vexen should fall relatively quickly. Be sure to heal if necessary, use any item cards in Sora's deck to restore used cards, and utilize the special abilities granted by any enemy cards to the fullest. Be patient and use careful timing when dodging the boss's attacks, as well.
Second battle
The second battle against Vexen is just as, if not more, difficult as the first battle. The boss will use the same attacks and sleights, so the same strategies can be used again to avoid them. Sora also should use the same deck he used during the first battle for the best chance of success, granted more cards can be added if Sora has increased his CP through battling Heartless before the battle. The only differences in this battle will be Vexen's two new enemy cards, the Air Pirate and Vexen, and a dangerous new sleight. This new sleight, Slide Break, will cause Vexen to elongate his Shield, increasing his attack range. He will then attempt to strike Sora twice before slamming the Shield down on the ground, creating an icy shockwave. Either Card Break the attack or chain several Dodge Rolls together to avoid it. While the Air Pirate enemy card will prevent Sora from Card Breaking Vexen's item cards, the Vexen enemy card has a particularly annoying ability. When it is used, Vexen will revive himself a single time after his first defeat, a great deal of HP restored to him. This will greatly increase the length of this all ready tedious battle, but do not fret, as the Vexen enemy card and its reviving capabilities will be Sora's prize for victory. As always, know when to heal, attack, and dodge. Be sure not to abuse sleights and to use enemy cards wisely, and Vexen should fall in due time with only moderate difficulty.
Reverse/Rebirth
The battle against Vexen in Reverse/Rebirth mode will be nearly identical to the boss's second battle with Sora in every aspect. The only differences will be Riku's greater power and speed overall, the presence of HP-restoring King Mickey friend cards, and the deadly sleights allowed because of Dark Mode. Vexen lastly has access to a new sleight, Diamond Dust. During this sleight's execution, Vexen will create an ice storm that covers the entire battlefield. Simply Card Break him to avoid the attack. While Riku's movements and abilities are slightly different than Sora's, the strategies for obtaining victory are the same. Simply wait for Riku to enter Dark Mode and use its powerful attacks and Sleights whenever possible. King Mickey cards will restore a great deal of HP, so this should be of no concern during the battle to the player. The player also may wish to stock King Mickey cards with two Soul Eater cards to perform either the Holy or Inverse Burst (depending on if Riku is in Dark Mode or not) sleight. This sleight, when executed, will allow Riku and Mickey to fire several spheres of light or darkness energy at Vexen, the attack having a long range and able to hit multiple times if not Card Broken. Riku also will be able to perform Card Duels, success allowing him to perform the powerful Maelstrom or Dark Maelstrom sleights. If one is patient and careful, Vexen will fall.
Kingdom Hearts II Final Mix
In Kingdom Hearts II Final Mix, the absence of cards completely changes Vexen's attack style. Fought as an Absent Silhouette, Sora must conquer the phantom version of this Nobody with Donald and Goofy at his side.
At the start of the battle, Vexen's Absent Silhouette will surround Sora in a stream of data. In a flash of light, the player will find Sora trapped within a massive block of ice. Rapidly press 
to set him free. Vexen's Absent Silhouette will then most likely attempt to hit Sora with twin, large snowflakes as they quickly spin around him. Dodge Roll multiple times or use Reflega to avoid the attack. The player can then attack the HP bar of the boss's Frozen Pride Shield. Depleting the weapon's HP will not only lower the boss's defenses, but it will also allow Sora to attack Vexen's Absent Silhouette himself. The player should use caution, however, for if the purple Data Bar at the top left of the screen should fill as Sora stands in the homing data stream Vexen's Absent Silhouette summoned at the start of the battle, a Clone Sora with its own HP bars to deplete will attack. This is merely a distraction method, but the Anti-Sora's attacks are powerful, and this power and its HP will only increase as the Data Bar fills from zero to five over the course of the battle. Thus, the player should make the Anti-Sora the first target. Otherwise, most combos the player attempts to use against Vexen will most likely be interrupted. Defeating a Clone Sora will relinquish MP orbs to restore any MP Sora has used up. One can then continue to hammer Vexen's Absent Silhouette with physical combos or even Fire spells. Should one attempt an aerial combo, however, the player must prepare for Vexen's Absent Silhouette to counter by shooting an icicle up from below Sora to halt the onslaught. Vexen will only use attacks the player has previously seen for the rest of the battle, so one should utilize the same strategies to avoid them as before.
All in all, the battle against Vexen's Absent Silhouette is not exceedingly difficult. One simply must, as with all boss battles, have patience. The player also should know when to dodge and to heal. Defeating any Clone Soras the boss creates should also become the first priority as soon as they spawn. The fact that the player must break through a constantly refilled HP bar just to get to the boss may be tedious, but a surprising amount of HP can be depleted before the Frozen Pride returns to Vexen's Absent Silhouette if one combines the usage of Fire spells with Sora's most powerful physical combos. The player should immediately go into Wisdom Form if they wish to attack Vexen with Fire or its upgrades, since this will boost the spell's power. An Ether should be used right before Sora's MP hits zero rather than afterwards. This will increase the amount of Fire spells that can be launched before Sora reverts to normal. Keep this up, and Vexen's Absent Silhouette will fall in due time.
Replica Data
The battle against Vexen's Replica Data will flow quite similarly to the battle against his Absent Silhouette. The only differences will be the amount of HP the boss has, the pattern in which he uses his attacks, and a deadly new ability that allows Vexen's Replica Data to summon large chunks of ice that will rotate around him and even rush at Sora before the boss creates a massive icicle. Comet can be used to avoid damage throughout this attack, although Sora will need to use an Ether and perform Comet again to last through the whole technique. Also, the Clone Sora's HP is relative to the amount of data that Vexen collects. Sora will receive a Lost Illusion as a reward for defeating the Replica Data.
Deck Statistics
Card types
| Attack card | Magic card | Item card A | Item card B | Enemy card A | Enemy card B | Enemy card C |
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Card values
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Sleights and attacks
| Attack | Description | Card |
| Shield Blow (シールドブロウ Shīrudo Burou) | Vexen slashes at Sora or Riku with the Frozen Pride, an icicle rising from below to damage them at the combo's end. In Chain of Memories, Vexen simply attacks Sora or Riku without causing an icicle to rise. | |
| Blizzara (ブリザラ Burizara) | Vexen sends a homing ice shard at Sora or Riku. | |
| Elixir (エリックサー Erikkusā) | Reloads all attack and magic cards. | |
| Mega-Ether (メガエーテル Mega Ēteru) | Quickly reloads magic cards with no charge time and resets the reload counter. Even normally unreloadable cards are restored. | |
| Sleight | Description | Requirements |
| Ice Needle (アイスニードル Aisu Nīdoru) | Vexen channels his power into the ground, creating icicles that shoot up from below and attack Sora or Riku. | + +
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| Freeze (フリーズ Furīzu) | Vexen focuses his power on Sora or Riku, encasing either character in ice and coming in close to attack, dealing additional damage. | + +
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| Ice Burn (アイスバーン Aisubān)[KH CoM] | Vexen creates pools of slippery ice on the ground that hinders Sora's movement. | + +
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| Slide Break (スライドブレイク Suraido Bureiku)[KH Re:CoM] | Vexen elongates the bottom of the Frozen Pride, transforming it into a monstrous ice blade. He then slashes Sora with the empowered weapon numerous times before performing a downward slam, thus shattering the ice blade and reverting his Shield to normal. | + +
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| Diamond Dust (ダイヤモンドダスト Daiamondo Dasuto) | Vexen creates an ice storm that slowly deals damage to Riku and covers the entire battlefield. | + +
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Videos
| Vexen I—Kingdom Hearts: Chain of Memories | Vexen II—Kingdom Hearts: Chain of Memories |
| <youtube width="320" height="240">dtACwFWl7jw</youtube> | <youtube width="320" height="240">7byT_76RQRY</youtube> |
| Vexen I—Kingdom Hearts Re:Chain of Memories | Vexen II—Kingdom Hearts Re:Chain of Memories |
| <youtube width="320" height="240">FIayCZZ7nZA</youtube> | <youtube width="320" height="240">QC-0UxsOqY4</youtube> |
| Vexen (Riku)—Kingdom Hearts: Chain of Memories | Vexen (Riku)—Kingdom Hearts Re:Chain of Memories |
| <youtube width="320" height="240">onAEvl0lnpc</youtube> | <youtube width="320" height="240">MpoQSrGAeJI</youtube> |
| Vexen's Absent Silhouette—Kingdom Hearts II Final Mix | Vexen's Data Replica—Kingdom Hearts II Final Mix |
| <youtube width="320" height="240">xg-sI1Xv5WU</youtube> | <youtube width="320" height="240">ItJcVFZ5XhY</youtube> |
| Nobodies |
|---|
| Organization XIII |
| I. Xemnas | II. Xigbar | III. Xaldin | IV. Vexen | V. Lexaeus | VI. Zexion | VII. Saïx | VIII. Axel | IX. Demyx | X. Luxord | XI. Marluxia | XII. Larxene | XIII. Roxas |
| Enemy Nobodies |
| Sorcerer - Sniper - Dragoon - Berserker - Assassin - Dancer - Gambler - Reaper - Ninja - Samurai Dusk - Creeper - Specter - Twilight Thorn - Fake Vivi |
| Special Nobodies |
| Naminé - Absent Silhouettes - Organization XIII's Replica Data - Anti-Saïx - Data-Roxas - Data-Naminé |