Kingdom Hearts Chain of Memories
Lexaeus's moves consist of him hitting the ground and causing earthquakes and Sleights. He also has a solid defense that prevents him from flinching when taking damage, though he does flinch after receiving a card break. Try to dodge his sleight, which can hit Riku multiple times. First focus on card breaking Lexaeus's cards to turn into Dark Mode and use sleights to deal heavy damage. Use MM Miracles or the Oogie Boogie card if low on HP. Use sleights while he is charging the reload card so he can't card break Riku, unless he is low on DP, then use as many sleights as possible.
Kingdom Hearts Re:Chain of Memories
In Re:Chain of Memories, most of Lexaeus's attacks are similar. He repeatedly strikes the ground and jagged rocks shoot up, attempting to impale Riku. A new attack is when Lexaeus starts to emit a yellow aura, during which his strength is temporarily increased, as well as his defense to which he doesn't flinch when taking damage. Using Dark Aura there can deal even more damage. He can do this a second time while it is already in effect, emitting a red aura, gaining another boost and becomes temporarily invulnerable to all attacks except card duel sleights. These buffs also allow him to use stronger sleights.
His first card is usually an eight, as is Riku's, so he has an immediate opportunity for a card duel. Use all the card duel opportunities as possible, as they do a lot of damage (one and a half bars). Focus on breaking his cards and then go in for the combos, because he will smash Riku with his axe sword if he gets too close. After the first card break or combo, Lexaeus will use his Enemy Card, use Parasite Cage to negate the effect. If choosing to focus on attacking him, Riku will have to side step every time Lexaeus attacks, to avoid being stunned. Use Dodge Roll to pick up Mickey cards. Use the Enemy Cards Maleficent (to power up cards) and Oogie Boogie (if low on HP). Another option is to wait for his attacks and try to card duel him; after the card duel, recharge the deck and repeat.
Since his power up in Re:Chain of Memories can be fatal if allowed to go through, a good approach to the battle is to prevent him from being able to power up. To do this the player should use Sleights, preferably through the lower valued cards (although it is still recommended to leave a few). Through this method, Lexaeus not only will be prevented from powering up but also from attacking, while accumulating DP quick. Once the player enters Dark Mode, the player should assault Lexaeus with Sleights, such as Dark Aura or Dark Break (hence why to leave a few low valued cards, otherwise a 0-7-7 combo can also work). These, in conjunction with the Maleficent Card, will deal a large amount of damage quick all the while stunning Lexaeus, thus greatly simplifying the battle. Riku may also wait until Lexaeus charges once to use Dark Aura while in Dark Mode, so that Lexaeus may not accidentally avoid a single strike due to the throwback he may have had if Dark Aura was used when he didn't Charge once.
Kingdom Hearts II Final Mix
During this battle, Sora and Lexaeus have a special power meter. Sora's power level is capped at 100, whereas Lexaeus steadily increases his power level throughout the fight, up to a maximum of 99999. As Lexaeus's power rises, his attack power, range, and defense increase.
Lexaeus has several moves in his arsenal. In one, he leaps upwards and slams the ground with his Skysplitter; evade this attack using Reflect or Dodge Roll. In another, he hurls the Skysplitter three times, each time causing rocks to erupt from the ground. The finisher is the most powerful of the three, but comes with an exploitable delay, allowing Sora to predict when to Dodge Roll. In the third attack, Lexaeus drags the Skysplitter on the ground to strike Sora. Blocking this attack with Guard or Reflect creates the opportunity to use the Mega-Impact Reaction command. When this command is used, Sora temporarily increases his power level by an amount equal to Lexaeus's current power level, striking Lexaeus and stripping him of his aura. After the Reaction Command is complete, Sora loses the power bonus.
Lexaeus steadily boosts his power level as his health dwindles. When increasing his power, he gains a red aura and pushes the party back. At higher power, Lexaeus's attacks gain further properties. For instance, when he drags the Skysplitter on the ground to strike Sora, the attack has more range on higher levels. Lexaeus can also charge at Sora, throw him against a stone pillar, and hurl his aura-infused Skysplitter at Sora. Alternately, he can grab Sora, throw him skyward, and slam him to the ground while pillars of earth erupt around the arena.
Lexaeus's ultimate attack involves him flying outside the arena for a number of seconds, before charging back into the arena. He finishes his attack by causing rocks to erupt over the entire arena. Sora should guard the charge and cast Reflect; alternately, High Jump and Glide around the arena.
The Oblivion and Decisive Pumpkin are crucial to bringing Lexaeus down quickly.
The Data Rematch plays out nearly identically to the Absent Silhouette battle. Lexaeus's health has greatly increased, and begins the fight with higher power.
To defeat the Data Replica, Sora should use the same strategy he used when taking on the original Absent Silhouette. However, while Sora has access to much more abilities than he had when taking down the Silhouette, Lexaeus is much stronger, and can employ countermeasures as well.
Notes and references