Zack is fought at Olympus Coliseum as a boss for both Terra and Aqua. Terra was tricked into fighting him the first time, thanks to Hades, and the Keyblade Wielder later battles Zack a second time to free him from the darkness and Hades's control. Zack then appears before Aqua in a friendly battle, serving as her final opponent in the Coliseum's tournament.
Victorious in the games, Terra has been tricked by Hades into fighting Zack. He will have access to Command Styles, D-Links, and Shotlocks, however, proper execution of these abilities will extremely decrease the difficulty of the battle.
At the beginning of the battle, Terra and the helmeted Zack will stand some distance from one another, both having the option of closing the gap with a long ranged attack. Zack will most likely be first to close the gap, attempting to damage Terra with a jumping, downward thrust. Slide can be used to avoid the attack, however, attacks such as Thunder Surge allowing the player to damage the boss while closing any gaps that form between him and Terra. Keeping in close range will decrease Zack's chances of using the jumping attack. If one remains far away from the boss, however, he will attempt to bombard Terra with a long-range dark fireball. Careful timing of Slide can be used to avoid it.
In terms of damaging Zack, it is best to keep Terra's excellence in physical strength in mind. It is also best to keep Zack off his feet. Thus, attacks such as Final Break are recommended. One can also use long-ranged physical and magical attacks such as Fire, the combination of magic and physical attacks having a strong chance of activating the Critical Impact Command Style. The powerful physical attacks granted by Critical Impact can easily deplete Zack's HP, so long as one is careful enough to Slide out of the way of his attacks to prevent taking damage.
Zack should be, overall, a very easy opponent to beat. So long as one remembers Terra's preference of brute strength, uses all benefits of D-Links, Shotlocks, and Command Styles, and heals if needed, Zack should fall in due time.
Zack, now under Hades's control, challenges Terra to a rematch. As within the first battle, Terra will have access to Command Styles, D-Links, and Shotlocks, proper execution of these abilities extremely decreasing the difficulty of the battle.
During the second battle against Zack, it is best that the player keep as far away from him as possible and remain in constant motion. A hit-and-run strategy is recommended, meaning attacks such as Thunder Surge and Fire should be favored. Zack will begin the battle by using several rapid slashes, chains of Slides are needed to be used in order to avoid the vicious combo, or the use of a Shotlock, as being caught in the attack will spell defeat or at least leave Terra's HP very low in the Alarm Zone. Zack may also use the jumping, downward thrust from the first battle. The same strategies can be used to avoid it, as well. Another new attack in Zack's arsenal is a devastating Meteor spell. This attack can easily be predicted, as his sword will always flash beforehand, and can easily be dodged with Slide. In terms of damaging Zack amidst all his dark and relentless attacks, one should wait until he pauses, struggling with the darkness that controls him. When this occurs, the player can then proceed to bombard Zack with physical attacks such as Critical Impact's combos or even a Final Break. Once Zack recollects himself after being damaged or from his struggles, it is important that the player resume the hit-and-run strategy. So long as one heals if necessary and uses all special abilities granted, Zack should not be a challenge to defeat.
Remembering that one's odds of surviving Zack's dark slash combo are slim to none if caught in it, and because it is very difficult to dodge, one way to avoid taking damage is to use a Shotlock command just as he begins his attack. The player will not take damage while using the Shotlock, and if Terra has full hit points, he should survive the barrage. Then, pummeling Zack to restore the Focus Gauge will ensure enough to keep using your Shotlock and survive. When Zack is done this attack, heal and keep pummeling him; finish this battle as fast as you can, while paying attention for more dark barrages and having the L and R triggers ready.
If the player is a head-on attacker and does not use Shotlocks and D-Links all that often, it is still possible to take Zack out in this form. Firaga, Mine Shield and Mine Square can stun Zack when used well. The player would also do well to have at least two Curagas in his deck.
Once More is a very useful ability to have against Zack's rapid slashes so that the player will be able to keep 1 HP before immediately curing himself. Another way of surviving these rapid slashes is by using Vanish: when Terra is invisible, Zack is likely to slash somewhere else and avoid Terra completely. This time can be used to heal and prepare the next command. Zack is also vulnerable to Zero Graviga if the player has it, so use that to either lick your wounds or press the offensive.
Zack challenges Aqua to a friendly battle, now free of Hades's control. If one has all ready beaten Terra's scenario, then the player will recognize many of Zack's attacks and know how to avoid them. However, Aqua favors magic over brute force, so this needs to be taken into account when calculating the best strategy. Aqua lastly has access to Shotlocks, Command Styles, and D-Links. These abilities should be used to the fullest extent.
Zack will begin the battle by launching a jumping, downward thrust attack. Cartwheel to avoid it. The player keeping at a hit-and-run strategy, they should bombard Zack in-between his attacks with Triple Blizzaga, Aero, or Fire. Mine Square can also be used to trip Zack, thus opening him to damage, if he is in close range. Careful positioning of Aqua may even cause Zack to land on the mines after executing his jumping thrust attack. Through the use of Aqua's many magic attacks, the Command Style Spellweaver will eventually activate. Closing gaps between Aqua and Zack with Thunder Surge or another Surge attack, the player should then begin to hit Zack with the more powerful physical attacks granted by the Command Style. Filling the Command Gauge even further may possibly upgrade the Command Style activated to an even stronger one, such as Bladecharge. If Bladecharge is indeed activated, physical attacks should be favored until the combo finisher appears. So long as special attacks are used to the fullest potential, one heals if necessary, and one keeps at a hit-and-run strategy while remembering Aqua's preference to magic, then Zack should fall in due time.
Rematches at the Mirage Arena
A Time To Chill
Zack, alongside Hades, makes a final stand in the A Time To Chill round of the Mirage Arena, fought after several waves of Unversed have been defeated. The only obvious change in the boss is his greatly increased HP. In terms of attacking, the player should first target Zack as his attacks can do large damage. Overall, the fight should be easy if one has a strong Keyblade, be at a high level, and tailors his or her strategy according to each character's strengths and weaknesses.
As in the second battle against Terra, Once More is necessary for this fight, and Vanish is extremely helpful.