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 earns the player a Secret Gem in the Japanese version of Kingdom Hearts Birth by Sleep, and the Void Gear in the North American, PAL, and Final Mix versions. The Vanitas Remnant also must be challenged if the player wishes to challenge the even more powerful Unknown. However, the player can simply unlock, and not defeat the Vanitas Remnant, and still be able to challenge the Unknown.

Story
Terra, Ventus, and Aqua separately return to the Badlands to find a mysterious sphere of dark energy hovering in the air. They each accept the challenge it presents, and the Vanitas Remnant then takes shape before them from another sphere of dark energy, much like the true Vanitas did during his creation, before drawing its Void Gear 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 reminiscent of Riku's Dark Mode, with faintly 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.

Attacks

 * Shadow Clone: Usually the first attack. The Remnant will encase itself in an impenetrable barrier while sending various shadow clones to slash at the player or slam down at the player before charging straight through the barrier. Inflicts Blind on contact
 * Dark Spiral: Speedy dashes in the air around the area while encased in dark energy. Will occur more often has the Remnant's HP dwindles
 * Dark Splicer: Slashes at the player while teleporting. Extends combo as HP dwindles
 * Dark Cannon: Shotlock passed down from Vanitas. Consists of firing an energy beam from three dark blue crystals. Remnant can rotate while using it
 * Shadow Dash + Dark Spikes: Dashes quickly in a circle around the player and summons spikes on each side of the player, which closes upon the player immediately. Will instantly kill the player, or leave them in critical condition while Blinded
 * Afterimage: Will leave an afterimage when caught in a combo or in mid-combo, and usually teleports above the player to retaliate
 * Χ-Blade combo: Charges Keyblade, then slashes at the player, and follows up with releasing an X-shaped crescent of energy which homes on the player. May leave an afterimage halfway through the combo
 * Strike: Simultaneously dashes and slashes at the player, and follows up with an upward somersault slash that releases a crescent of dark energy, which homes on the player and inflicts Confuse status upon contact.
 * Jumping Blizzaga: Downward strike on the player upon teleporting above them, and simultaneously casting Blizzaga
 * Erupt + Firaga: Dives straight into the ground, and homes in on the player in a pool of dark energy. Upon reaching the player, the Remnant will erupt from the ground while casting multiple Firagas to rain down on the player
 * Flame Burst: Charges up and fires a fireball at the player, which then splits into three and homes in on the player.
 * Dark Thundaga:- Simultaneously initiating a downward strike at the player and casting Thundaga
 * Cure: Will be cast if the Remnant witnesses the player casting the same spell.

The player cannot use D-Links, but has access to Command Styles and Shotlocks. However, Shotlocks have little effect on the Remnant, as it will constantly use Jumping Blizzaga and Afterimage to avoid it. Therefore, Shotlocks may be used to escape the Remnant's attacks, making them most useful when maxed. The Keyblade choice is dependent on which commands are being used to defeat the Remnant—a high strength Keyblade if the protagonist is focusing on Aerial Slam, or a high magic Keyblade if they are focusing on Tornado or Seeker Mine. Use the basic form of the protagonist's dodging commands, as the offensive forms do not offer the needed periods of invincibility. As using Cure or Friend Cure spells will allow the Remnant to heal, the protagonist should rely on Heal Strike, Renewal Block or Renewal Barrier, and Potions for rejuvenation.

Terra
While Terra receives a boost in strength, he is hampered by his slow speed and poor dodging ability. The player should have Once More, Second Chance, and HP Boost equipped. It's recommended that the player evolve Terra's Finish Command to Demolition, as it makes Terra invulnerable and can damage the Remnant. Since Terra is a master of using earth-related magic, it's recommended that the player use Mine Square or Mine Shield. The player can also use Brutal Blast or Quake, but should be careful when casting them as it takes time, and the Remnant can potentially defeat you. Sonic Impact for Terra may be useful for disrupting the Remnant's attacks, but leaves Terra vulnerable while using it, so the player should only use it to disrupt attacks instead of dodging. So long as the player remembers that Terra prefers strength over speed, the Remnant will be defeated.

Ventus
While Ven has low strength, his speed allows him to compensate for that, and is key for winning the battle against the Remnant. Since he is very experienced with casting Aero-based magic, attacks like Tornado Strike and Tornado should be used. However, the Tornado spell has the disadvantage of immobilizing Ven while casting it, making it very difficult to predict the timing of the spell. Another attack that can damage the Remnant is Ven's Wind Raid, which can score multiple hits before returning to Ven's hand. Like the Tornado spell however, it can immobilize Ven for a few seconds. The Remnant is also vulnerable to Ven's Counter Rush, and some of his charged attacks can be avoided with Reversal, and countered with Reversal Slash. It's recommended that Ventus's Finish Command should be Air Flair 4, which is a series of quick strikes while casting Aero with each strike, or evolve their Finisher to the more powerful Stratosphere, which allows Ven to jump in the air to avoid attacks. Should the player remember that Ven favors speed, and maintains the proper hit-and-run strategy, as well as healing when necessary, the Remnant should fall in due time.

Aqua
Aqua has average speed and strength, but her real strength lies in using magic. It's recommended to fill the Command Deck with magic commands as well as Potions. It's recommended that the Finish Command is Magic Pulse 4, which causes the Remnant to be knocked into the air, or Teleport Spike, which grants invincibility while attacking. Unlike the other two characters, Aqua can use Seeker Mine, which can home in on the player and produce the same effects as other Mine-related attacks. The Remnant is vulnerable to Aqua's Counter Blast, and its attacks can be avoided by teleporting behind it if the Teleport ability is equipped. The player should also use Aqua's Doubleflight and Barrier in midair to avoid the Remnant's attacks, which are mostly occurring on the ground. Raging Storm is very useful as it knocks the Remnant into the air and inflicts damage on contact. Unfortunately, Aqua can still be damaged by any of the Remnant's attacks while using Raging Storm. Aqua's Barrier Surge should also be equipped to block attacks as well as getting in close with the Remnant. Should the player remember Aqua's fighting style, the Remnant can be defeated with ease.

All
A glitch in the Remnant's A.I. can provide an easy victory to those experiencing difficulty in taking victory. A column of rock in the battlefield's corner is shaped such that luring the Remnant to it and retreating to the opposite side will cause it to consistently run straight towards the player without attacking. By filling the Command Deck completely with Strike Raid attacks, or similar variants, and ensuring the player is Locked-On to the Remnant, the attack will pass through the column of stone and connect with the Remnant.

Terra's strength is the strongest of the three, and as such he can easily do twice as much damage with a basic Strike Raid than Ventus or Aqua. Ventus' variant Wind Raid can land multiple hits per throw, and can be used more efficiently than other Raid commands. As Aqua's stats are heavily inclined towards magic, it is best to save this particular strategy as a last resort.

The prize for defeating the Vanitas Remnant, regardless of character used, is a Secret Gem in the original Japanese release of Kingdom Hearts Birth by Sleep. The Void Gear Keyblade is rewarded to the player in the North American and Final Mix versions.