Secret Boss Rush Guide (KH 0.2 Birth by Sleep)

After creating a Save File with Clear Data, additional Treasure Chests become available, containing the 12 Zodiac Relics. Once you collect them all and return to The World Within, a new mirror will appear in the center of the main room.

Examining this mirror will enter you into the Secret Boss Rush, a series of consecutive battles you must clear all in one go in order to complete Objective 42 and acquire the Tiara Wardrobe Piece. It is highly recommended that Aqua be level 70 at the very least, as the enemies inside the mirror are much more powerful than any you’ll encounter elsewhere in the game. Even at higher levels, the Secret Boss Rush will be grueling and difficult, to say the least.

Darkside
This battle against Darkside is exactly like the first battle against him in the the Forest of Thorns. The only major differences to note are that Darkside can now summon Neoshadows and Flutterings in addition to the usual Shadows. There are also a lot more dark orbs that fall from the sky, so keep an eye on how they drain your HP.
Victory Reward: —

Heartless (Wave 1)
The next stage is a battle against a massive wave of Heartless. Specifically, this battle pits you up against Flame Cores, Water Cores, and Earth Cores. The Flame Cores will be your most immediate concern, so try to focus on them near the beginning of the battle. Make sure to keep the Earth Cores in check though, as they can hit you and leave you stunned, which could cost you the battle. The Water Cores will show up toward the end of the battle, so be on the lookout for them as you're finishing up.
Victory Reward: —

Heartless (Wave 1)

The next stage is a battle against a massive wave of Heartless. Specifically, this battle pits you up against Flame Cores, Water Cores, and Earth Cores.

The Flame Cores will be your most immediate concern, so try to focus on them near the beginning of the battle. Make sure to keep the Earth Cores in check though, as they can hit you and leave you stunned, which could cost you the battle. The Water Cores will show up toward the end of the battle, so be on the lookout for them as you're finishing up.

Victory Reward: —

Heartless (Wave 2)
Another wave of Heartless awaits you after clearing the first, this time featuring Shadows, Flutterings, and Neoshadows. This is arguably an easier battle than the last, but the Flutterings and Neoshadows frequently attack by lunging across the room, so it's very easy to be hit from out of nowhere. Be careful!
Victory Reward: —

Demon Tower
This battle plays out like any other battle against the Demon Tower in the past, though it's a lot more relentless and powerful than any time before. You'll need to rely on quick Blocks and Cartwheels to avoid taking damage, while using any opportunity it gives you to land hits of your own. Magic is especially helpful for trying to land hits while the Demon Tower is moving erratically.
Victory Reward: —

Zodiac Phantom Aqua
We're just going to come right out and say it: this fight is ridiculous! It is quite possibly even harder than the Demon Tide on Critical Mode, and that's while playing on Beginner Mode! Zodiac Phantom Aqua's attacks are far more aggressive, she warps around the room way more frequently than any of your previous battles against her, and many of her attacks can't even be blocked! Openings to attack Zodiac Phantom Aqua are few and far between, meaning you're going to be spending much of this battle on defense. Any of Zodiac Phantom Aqua's attacks that give off a red glow are incapable of being blocked, so you'll need to use the Cartwheel to evade them as best you can. If Zodiac Phantom Aqua ever paces around (as she's done in previous battles), DON'T engage her, as this is baiting you into taking some heavy blows that you can't avoid! Instead, just wait her out until she goes back on the offensive. As the battle carries on, and you whittle her HP down to about 2 bars left, Zodiac Phantom Aqua will enter Spellweaver (much like she did during your third battle against her in The World Within. Her attacks become much more aggressive and her openings become even harder to take advantage of. Many of her onslaughts during this segment of the battle are laced with a red glow, making them impossible to block. Your best bet is to Cartwheel all around and hope for the best. You're best chance to deal some serious damage to her is during her Spellweaver Finish. Block the initial hits, and then use Counter Blast to strike her off-guard right as she finishes. This is your chance to land a full 2 combos before she goes back on the offensive, IF you manage to time it just right!
Victory Reward: Max MP +10

Zodiac Phantom Aqua

We're just going to come right out and say it: this fight is ridiculous! It is quite possibly even harder than the Demon Tide on Critical Mode, and that's while playing on Beginner Mode! Zodiac Phantom Aqua's attacks are far more aggressive, she warps around the room way more frequently than any of your previous battles against her, and many of her attacks can't even be blocked!

Openings to attack Zodiac Phantom Aqua are few and far between, meaning you're going to be spending much of this battle on defense. Any of Zodiac Phantom Aqua's attacks that give off a red glow are incapable of being blocked, so you'll need to use the Cartwheel to evade them as best you can.

If Zodiac Phantom Aqua ever paces around (as she's done in previous battles), DON'T engage her, as this is baiting you into taking some heavy blows that you can't avoid! Instead, just wait her out until she goes back on the offensive.

As the battle carries on, and you whittle her HP down to about 2 bars left, Zodiac Phantom Aqua will enter Spellweaver (much like she did during your third battle against her in The World Within. Her attacks become much more aggressive and her openings become even harder to take advantage of. Many of her onslaughts during this segment of the battle are laced with a red glow, making them impossible to block. Your best bet is to Cartwheel all around and hope for the best.

You're best chance to deal some serious damage to her is during her Spellweaver Finish. Block the initial hits, and then use Counter Blast to strike her off-guard right as she finishes. This is your chance to land a full 2 combos before she goes back on the offensive, IF you manage to time it just right!

Victory Reward: Max MP +10