Doppelganger

The Doppelganger is a creature which takes the form of another, usually its victims. The idea of humans having doppelgängers comes from Egyptian mythology. It is said that if someone ever meets their doppelgänger, its intent is to murder him or her so it can take over their role in life.

Origins
A doppelgänger is a look-alike or double of a living person who is sometimes portrayed as a harbinger of bad luck. In some traditions, a doppelgänger seen by a person's relative or friend portends illness or danger, while seeing one's own doppelgänger is said to be an omen of death. The word "doppelgänger" is a loanword from German "Doppelgänger", consisting of the two substantives Doppel (double) Gänger (walker or goer).

In Ancient Egyptian mythology, a ka was a tangible "spirit double" having the same memories and feelings as the person to whom the counterpart belongs.

Castlevania III: Dracula's Curse
The Doppelganger was first introduced into the series at the end of the villa stage in Dracula's Curse. It takes the form of whoever character the player is playing with at the moment (either Trevor, Sypha, Grant or Alucard), and attack constantly while homing in on the hero. If the player selects another character while in battle, the Doppelganger will also take his or her form. This allows for some strategy, letting the player move to a better position and counter-attack while the Doppelganger is in its morphing animation; or letting the player choose which form to fight against.

Castlevania Chronicles
The Doppelganger will form from Simon's reflection on a mirror, and break out of it to attack. Again, it will attack relentlessly while homing in on the player. Upon defeat, the Doppelganger will vomit a barrage of mirror shards while struggling for his life.

Castlevania: Symphony of the Night
The Doppelganger boss has the form of Alucard and appears twice in the game:
 * Doppleganger10 is the second boss of the game (third if counting Dracula from the prologue). It uses a Short Sword and the Dagger sub-weapon, and can turn into mist and bat before Alucard can. The stopwatch can make this fight trivial, completely freezing the Doppelganger. It is then at the mercy of Alucard's attacks, as it will not have invulnerability upon taking damage. On the other hand, though, the player should avoid using the stopwatch right after hitting the Doppelganger; if they do, it will be stuck in its invulnerability state for the duration of the effect.


 * Doppleganger40 is a stronger doppelganger with new moves. He can use the Rebound Stone sub-weapon, is equipped with the Gravity Boots and the Leap Stone, as well as having all of Doppelganger10's abilities. In addition, Doppelganger40 will use whatever weapon Alucard is using, allowing for some strategy (such as using Terminus Est to have him do poison damage, while having the Topaz Circlet equipped, so the Doppelganger's attacks heal Alucard instead of damaging him).

Both Doppelgangers have very limited artificial intelligence, however, which can be exploited. Just running in their direction, jumping and attacking in mid-air will make the Doppelgangers take damage and get knocked back, allowing to repeat the same process again and again until they die.

Castlevania: Lament of Innocence
The Doppelganger boss (referred to as "Leon Fake" in Joachim Mode) is fought twice in this game, where it serves as a mid-boss for both levels in which it appears.

The Doppelganger is first encountered in the Dark Palace of Waterfalls. Here, he utilizes a copy of Leon's Whip of Alchemy and a variety of other attacks. The Doppelganger can quick-step, execute a three-attack or seven-attack combo using the whip, execute a flaming leap charge that propels the Doppelganger forward, throw holy water either at its feet or toward Leon, or use a duplicate of Leon's Cross Blazer (Holy Water + Purple Orb) attack, causing a cross-shaped flame to erupt around it. In Crazy Mode, Leon must simultaneously battle two Doppelgangers, both of whom utilize this move-set. After defeat, the Doppelganger will flee into the sewers.

The Doppelganger reappears as the mid-boss of the Pagoda of the Misty Moon. Palette-swapped with a red tint, the Doppelganger boasts more health than in the previous encounter, and has abandoned its copy of the Whip of Alchemy in favor of flaming fist attacks. While still retaining its quick-step ability and its three holy water-based attacks, the Doppelganger has replaced its whip attacks and leap charge with four melee attacks: a downward kick, a fast two-hit punch combo, a single punch, or a three-attack punch combo.

Castlevania: Dawn of Sorrow
While the player does not physically fight the Doppelganger in this game, Soma can obtain a Doppelganger soul in the Garden of Madness that allows him to switch between two sets of weapons, souls and armor quickly. A Doppelganger also appears in the center of the castle in the garden, where it takes the form of Mina Hakuba. In a gambit to turn Soma into the Dark Lord, Celia Fortner kills this Doppelganger, enraging Soma, though Arikado arrives in time to inform Soma of the truth. Shortly after, the soul of Dmitrii Blinov escapes Soma's body and inhabits the body of the slain Doppelganger, using it to revive himself.

Castlevania: Curse of Darkness
While no Doppelganger makes a canonical appearance in this game, in Trevor Mode, both Trevor boss fights are replaced by battles with the Trevor Doppelganger. The Trevor Doppelganger fights exactly as Trevor fought in the main game, though it is differentiated from Trevor by his pale blue hue and weakness to light. Additionally, during the first fight, its health must be depleted entirely, rather than one-fourth depleted as in the first Trevor fight. During the second encounter with the Doppelganger, it is also resistant to the Dark element.

Castlevania: Portrait of Ruin
The Doppelganger can be found in the deepest level of the Nest of Evil. Generally, whichever character is the stronger and better-equipped is the one the Doppelganger will become.

To drastically decrease the difficulty of this battle, the player can remove all equipment from both of their characters before entering the room and re-equip the items after entering the room, as the Doppelganger will only copy the player's equipment as it was when they entered. To increase the difficulty, the opposite can be done, and players can wear their best equipment upon entering the room.

No matter the Doppelganger's strength, a good tactic for starting the fight is to make use of 1,000 Blades immediately upon entering. Doing so will inflict many hits, usually up to the point where the Doppelganger will go into hit recovery. It may even be slightly knocked back if the hits prove powerful enough. In contrast to other games, coming into contact with the Doppelganger will not deal any collision damage. After the Doppelganger is killed in the Jonathan-Charlotte campaign, the player can acquire the final Dual Crush skill, Greatest Five.

Pachislot Akumajō Dracula III
Trevor's Doppelganger can be found in this game.

Trivia

 * Shadow, a boss which appears in Castlevania: Harmony of Dissonance, is basically another type of doppelganger. However, instead of copying and adopting the form of the protagonist, it takes the form of a Black Panther, a Moth and an Evil Sword.