Vanitas Remnant

The Vanitas Remnant makes its first and only appearance as a secret, optional boss in Kingdom Hearts Birth by Sleep. After the player clears the Final Episode, a crest similar to an Absent Silhouette portal will appear in the Badlands area of the Keyblade Graveyard. Simply approach the portal and select the "That's a danger I'm willing to face" option to initiate the battle. Defeating the Vanitas Remnant will earn the player a Secret Gem in the Japanese version of Kingdom Hearts Birth by Sleep, and the Void Gear Keyblade in North American and European versions. The Void Gear will also be the player's prize for defeating the boss in Kingdom Hearts Birth by Sleep Final Mix. The Vanitas Remnant also must be defeated if the player wishes to challenge the even more powerful Unknown.

Story
Terra, Ventus, or Aqua returns to the Badlands to find a mysterious sphere of dark energy hovering in the air in front of a large pillar of rock that was not present during their last visit to the area. They ignore the dark power felt emanating from the crest, accepting the challenge it presents. The Vanitas Remnant then takes shape behind them from a sphere of dark energy, much like the true Vanitas did during his creation, drawing its Void Gear Keyblade and attacking. After the Remnant's defeat, it transforms back into the dark energy sphere from which it originally spawned and vanishes.

Design
The Vanitas Remnant, true to its name, is a palette swap of the helmeted Vanitas. Its smooth helmet is completely black with an Unversed insignia emblazoned on it. Its torso and legs are covered by a black bodysuit with nearly glowing white highlights on the chest. The material over its arms shifts in color from black to grey to white, before shifting to black again on the palms of its hands. Its boots are white with black soles. It also wears a white, skirt-like garment with black tips around its waist, held up by several grey straps.

The crest that must be approached by the player to begin the battle has a very similar appearance to an Absent Silhouette portal, varying shades of purple in coloration with shards of black, rock-like material floating around it. The symbol appearing on the crest displays two halves of a gear which join to form an "S", the Keychain of the Void Gear Keyblade, both Vanitas and his Remnant's primary weapon.

Aqua
The Vanitas Remnant is probably the easiest to defeat without the use of the glitch in the Remnant's A.I. as Aqua. This is simply because her normal Cartwheel ability grants her some level of invulnerability to its attacks, something Terra's Slide and Ventus's Dodge Roll lack. Deactivate any advanced forms of Cartwheel before the battle, as they have a shorter period of invulnerability. Also be sure to replace all advanced Commands in your Command Deck with at least three sets of Mega-Potions (taking up three of the available eight slots). Fill four of the remaining open slots with Fabracadabra items, and fill the last slot with Seeker Mine (a Command unique to Aqua that can be obtained by melding Mine Square with Mine Shield). The Vanitas Remnant is beatable at any level (granted it is 40 or higher), but only if the player uses this specific Command Deck and has both the Second Chance and Once More abilities equipped. It is also advised that the player equip all three levels of HP Boost, as well. The player's choice of Keyblade does not matter, but the Ultima Weapon is recommended for use if the player wishes to deal the most damage possible in both physical and magical attacks. If the player has yet to obtain the Ultima Weapon, Stormfall can be used as a good alternative due to its even boosts to Aqua's stats.

The first thing the player should do at the start of the battle is attempt to attack the Vanitas Remnant in order to prevent him from using his shadow attack. If the player lands an unlikely hit, immediately Cartwheel away to prevent taking damage from the possible counter attack. If the player misses, then the Remnant will either use a two-hit combo that sends a homing crescent-shaped wave of energy at Aqua (use Aqua's Payback ability to damage Vanitas, and then avoid the energy wave with Cartwheel if possible. Note that failure to do so has a 100% chance of giving Aqua the Confused status effect), begin the true Vanitas's X-blade combo (a forward lunge followed by a downward surge of energy ended by a combo finisher which causes the boss to launch an X-shaped energy wave at the player. Use a chain of Cartwheels to avoid this attack), or it may leap back and sink into the ground to perform Vanitas's upward lunge from the pool of darkness that represents it, granted this time the attack adds the spawning of numerous fireballs to the mix (this attack can be avoided through a chain of Cartwheels and leaves the boss temporarily vulnerable to an attack of the player's).

The Vanitas Remnant will mainly use these three attacks (as well as the shadow attack, which can be avoided through chaining multiple Cartwheels together so long as the player traverses away from the boss to avoid his lunging combo finisher) for a majority of the battle. If it shouts "Darkness waits!" and lunges at Aqua while airborne, be prepared to Cartwheel numerous times to avoid each of the following lunges (only a single Cartwheel is necessary to avoid each lunge). The boss also may rush at Aqua, causing several dark crystals to appear behind him that will then rush at Aqua as the screen blackens (a well-timed Cartwheel during this attack's execution can prevent taking damage). The Vanitas Remnant will remain stationary for a time after this attack is used, so use this opening to lay a trap of Seeker Mines. The boss may blunder into them during a simple run to reach Aqua, his X-blade combo, or even his teleporting slash attacks. The homing Mines will deplete a great deal of HP from the boss's single HP bar (granted all if not most of the Mines hit). If the boss attempts to hit Aqua with a downward counter attack that spawns three large pillars of ice (a common side-effect of being hit with Seeker Mine), Cartwheel to avoid it. Should the Vanitas Remnant continue the offensive and interrupt a slashing combo to launch a fireball, immediately chain together Cartwheels to avoid the three smaller, homing fireballs that follow.

Once about three quarters of the boss's HP has been depleted through the laying of Seeker Mines (a time-consuming strategy since the player must wait for an opening after the boss's upward rush attack or dark crystal attack to lay them and spend the rest of the time dodging in hopes that the boss comes in contact with the Mines), the player may activate the Spellweaver Command Style through the usage of a Fabracadabra. Immediately use a second if an opening is present to instantly gain access to the Command Style's finisher. While not particularly powerful, the "Spellweaver" Deck Command makes Aqua invincible, has a great range, and can hit the Vanitas Remnant multiple times. The usage of "Spellweaver" can easily depelte a large portion of HP if the player's Attack stat is high enough. Otherwise, the player can continue to combine Spellweavers with Seeker Mines until the Vanitas Remnant is defeated. Granted this is a time-consuming strategy, it almost always has a chance of being successful, so long as the player finds openings in which a Mega-Potion can be used if Aqua is low on HP. Do not get discouraged if Aqua is defeated, as repeated attempts will help the player learn good strategies to use in terms of avoiding the Vanitas Remnant's attacks. Correct methods of dodging, when combined with this Command Deck, will ensure victory eventually if it is not obtained on the first playthrough. If all else fails, the player can take advantage of the Vanitas Remnant's A.I. glitch, granted Aqua's Strike Raids are weakest of the playable trio, increasing the length and monotonousness of the battle a great deal. So long as the player and Vanitas Remnant remain on opposite sides of the large boulder in the corner of the battlefield and the player stays Locked-On to the boss (the only way Strike Raid will hit), the player will be ensured a victory on the first playthrough.

Aqua's prize for defeating the Vanitas Remnant, as with Terra and Ventus, will be a Secret Gem in the Japanese version of Kingdom Hearts Birth by Sleep and the Void Gear Keyblade in the English version. The Void Gear will also be the player's prize for defeating the Vanitas Remnant in Kingdom Hearts Birth by Sleep Final Mix. Additionally, the Unknown will appear in the Land of Departure to present the player with an even more challenging boss fight.