- "This is Doppelganger, a symbol of death that wanders around the area. Be on guard when dark clouds appear on screen. He is coming at you from the direction of the red arrow. He is very powerful so run before he catches you."
- — The World R:2 —
A Doppelganger (ドッペルゲンガー) is a special monster in The World R:2. If a player avoids battling for five minutes on a field, or if they go to a field with the 3rd keyword Moonlight, a darkness-shrouded version of that character's PC will appear and attack them. Doppelganger starts off eight levels higher than the player and draws its stats from what the player's would be at that same level if they were unaltered by items. Doppelganger's level is capped at whatever the maximum level is for that volume: 50 for Rebirth, 100 for Reminisce, 150 for Redemption. This is proven by the fact that Doppelganger becomes vulnerable to offensive weapon effects outside of Beast Awakening when the player reaches at least (level cap - 4), and the fact that its maximum HP growth halts after the player reaches (level cap - 8).
In addition, Doppelganger uses custom equipment different from that it drops, including Heine's Invasion, Heine's Shadow, Heine's Zero, and Dopple Dual Gun for weapons, Pale Friend, Silent Night, and Other Self for armors, and Truly Feared, Great Suffering, and Shadow for accessories. The armor and accessory used are determined by which volume of G.U. one is playing, while the weapon is determined by whatever the player is using. For weapons, the effects are the same as the real weapons that can be acquired in volume 2 in Rebirth, but in Reminisce and Redemption, Doppelganger's weapons copy the effects of the player's weapon if it is ultra rare (Rarity *5); it cannot copy common weapons, and in those cases, the weapons have no special effects. Doppelganger's armor effects consist of Physical -75% and Magic -75% in Rebirth and Reminisce, while Damage Change is added to those effects in Redemption. Its accessory effects are always Speed +50% and custom HP regeneration (+ (max HP ÷ 50) at every interval). Doppelganger also has an inherent defense against being stunned by the impact of hits it takes and being knocked into the air.
The skills Doppelganger has available are whatever the player has available at their current weapon level; in the case of Adept Rogues, only for their current weapon. They also carry the spell Ma Repth, which heals 300 HP, no matter who they face. This spell is only used at low HP.
Defeating Doppelganger earns the player the Own King key item in Rebirth. In Reminisce, the player receives Heine's Shadow and the Forgotten Shadow key item, along with Heine's Invasion if the Own King is present in Key Item inventory, for the first victory. A second defeat in that volume bestows upon the victor Moonlight Faith and Heine's Zero. In Redemption, the reward depends on when Doppelganger is defeated. If this occurs prior to achieving Xth Form, only the Bygone Servant key item will be dropped. If Haseo has attained Xth Form, he will earn Bygone Servant if he doesn't have it, along with the DG-0. If the main storyline is finished, Bygone Servant and DG-0 will be dropped if they have yet to be acquired, after which, if the player has Own King, Forgotten Shadow, and Moonlight Faith as well, the armor Other Self and the accessory Shadow will be awarded. The four key items related to Doppelganger will then be destroyed. If Doppelganger has no unique rewards left, a Mission Reward item for the area will be the result. A Mission Reward item may also be earned with one of the unique rewards if Doppelganger is hit by a Steam Bike equipped with Wish Filefish and/or Wish Peeler to start off the battle.
- * Determined by level
- ** Will not exceed the current volume's level cap
- Doppelganger only changes weapons, and therefore his weapon effects, when the player changes weapon types. It is therefore very easy to confuse a Doppelganger into using a weapon with no effects against an ultra rare weapon in the latter two volumes.
- Doppelganger can change weapons at any time, even in the middle of a skill.
- The Anti-Existence monsters are often referred to as Doppelgangers because they look and act the same, despite obvious stat, equipment, and protection differences.
- Another Doppelganger appears in .hack//Link. Inside a dungeon, called the Final Labyrinth, phantom monsters taking the shape of Kite and his old companions will appear to battle Tokio.