Game:Demyx

Demyx is fought as a boss in Kingdom Hearts II. He attacks Sora and his allies in the Underworld, as well as in Hollow Bastion during the Battle of the 1000 Heartless. He can be fought again in a data rematch in Kingdom Hearts II Final Mix.

First encounter
During the first battle, Demyx does not physically attack. Instead, he summons 100 water forms that must be defeated within a time limit. To make this battle a success, it's recommended to use the "Wild Dance" Reaction Command as well as the Fire spell as many times as possible. Ethers should be brought into battle to refill the MP Gauge after a consecutive round of Fire spells, but HP should not be a problem, as defeating the water forms causes HP Balls to drop.

Second encounter
Attacks Despite claiming to be a lousy fighter, Demyx tends to be a long and usually frustrating opponent. When the fight begins, Demyx summons his "water forms", and Sora has forty seconds to destroy fifty of them. There are two types of water forms—those shaped like musical notes, and those shaped like Demyx. Striking the Demyx-shaped water forms will cause them to transform into note-shaped ones. The note water forms can be grabbed with the Reaction Command Wild Dance, which causes damage to many water forms over a large area. Limit commands also help to destroy the water forms quickly.
 * Water Dash: Dashes forward leaving pillars of water behind and ending with a circle of pillars around him.
 * Bubble Blaster: Rapidly shoots bubbles at the enemy
 * Bubble Drop: Drops bubbles onto the foe
 * Form Summon: Summons water forms to fight
 * Wall Walk: Walks toward Sora with a wall of water pillars in front of him
 * Water Finish: After yelling,"Get to the beat!," Demyx strikes Sora with his Sitar a couple times, sending out pillars, and then ending with a blast of many pillars
 * Pillar Cast: Casts a line of pillars that chases Sora

After the forms are destroyed, Demyx begins his normal attacks. He will leap across the arena, spouts of water erupting from the ground in his wake, and he will summon pillars of water around him. If you can hit him with a combo finisher before he leaps again you can stop him. Demyx can leap and summon water even when knocked into the air by a combo, so be careful attacking him in the air. Demyx will also summon a rain of bubbles from above, and fire a bombardment of bubbles at Sora directly. He can also summon several spheres of water around himself, which then follow Sora, then explode after a short delay, although Sora has a brief period to escape before detonation. Demyx will often summon two or three note-shaped water forms as back-up during the battle, and while there is no timer, these water forms will attack Sora and can cause heavy damage, although Sora may use the reaction command to destroy them and cause collateral damage to Demyx.

Sora may occasionally get the chance to use the Show Stealer command (signified by Demyx marching toward Sora while playing his sitar and quipping "Ain't it a blast?" ), which knocks Demyx into the air and stuns him for a short time. This can backfire, however, as hitting Demyx without triggering the Show Stealer will result in Demyx automatically counter-attacking with his sitar and doing major damage.

When he has lost approximately half his health, Demyx will summon more water forms, and Sora must defeat ten of them in ten seconds. This is difficult, but possible. Afterwards, Demyx resumes his normal attacks, but also gains a new technique. He will walk towards Sora, swinging his sitar, summoning walls of water in front of him. However, if you Sora uses Guard against Demyx's sitar, Sora will not be damaged by the pillars, due to the brief invincibility from a successful Guard, allowing Sora to counterattack afterwards.

Most of Demyx's attacks knock Sora into the air, so the Aerial Recovery ability is very useful. It is highly advised that you keep your distance from Demyx until you have a clear opening to attack. For this reason, Thunder helps greatly, and Wisdom Form is also useful.

An alternate method is to beat all the water forms in the beginning, but then immediately after use Knocksmash, this takes his health down almost completely for an extremely easy win, without using any other magic or drive forms.

Data Rematch
Demyx fights in a similar manner to the previous battle, but this time, he makes use of more water clones. There are four rounds of water clones (before Sora first gets to damage Demyx), and Sora must destroy all of them in thirty seconds, without using the Reaction Command Wild Dance. The final round has 99 clones, when Demyx has one bar of HP left. Also, Demyx's fountains increase in number and in power and some briefly follow Sora, which somewhat resembles Vexen's Ice Needles Sleight.

The data rematch can be accessed in the Garden of Assemblage in Radiant Garden. It is advisable to stock up on Ethers/Elixirs or any MP-restoring items in the item slots (Donald's and Goofy's slots too), and get Donald and Goofy to carry out their attacks very frequently (note: do not configure their attacks to "well-balanced" or "rarely", as one might need their magic attacks). Also, disable Auto-Limit, as this might prevent usage of the Reaction Command Wild Dance and might force one into Limit mode instead, making it more difficult to destroy all the clones on time. In the data rematch, the note-shaped water clones do not appear, but casting Blizzaga on the Demyx water clones will turn them into notes and allows the use of Wild Dance. Firaga will also instantly destroy the water clones. Switch to Limit Form and use Ragnarok.

Alternatively, switch to Wisdom Form and use magic-based attacks (hence it is necessary to stock up Ethers and such). Reflect and Fire will come in handy—and while in in Wisdom Form, casting magic is done at a faster rate, and one can move around quicker to destroy more water clones.

Also, be sure to reset the Anti-Points counter to zero before entering into this battle, so as to help prevent Sora from entering Anti-Form. However, one attack from Anti-Form can destroy a water clone, so the choice is up to the player.

Heal when necessary, but prioritize MP for attacks.