Guide to defeating doppelganger

The following tactics have been suggested to best the Doppelganger:

General Tips:

 * In general, the doppelganger will equip the same skills you equip, so don't equip any skill you wouldn't want used against you.
 * Think very carefully before bringing any skill that can be used to heal yourself.
 * Equip lots of slow-casting self-buffs: the less useful in the one-on-one fight, the better. The AI will waste time at the beginning of the fight casting every buff on itself.
 * For all ranged attackers, stay on higher ground. Ranged attacks from higher to lower ground do more damage.
 * Cast any self-buff enchantments before stepping on the third stone that starts the cutscene. It will last into the match.

Elementalist Tips:

 * Equip ranged area-of-effect damage-over-time spells such as Fire Storm and Meteor Shower. When these are used against you, you can just move out of the area of effect, while the AI is often not smart enough to do so.

Mesmer Tips:

 * Bring Backfire and Empathy. The AI is not smart enough to refrain from casting / attacking while hexed with those skills and will quickly kill itself.

Monk Tips:

 * Equip Healing Breeze. The AI currently will not use Healing Breeze for ordinary healing.  If your Healing Prayers attribute is 12 or higher the healing will be able to keep pace with the doppelganger's weapon damage.
 * Bring smiting spells. You can reportedly cast them faster than the AI will. You can easily defeat the Mirror Self by only using Zealot's Fire and Reversal of Fortune.
 * Bring useless maintenance spells. If you bring at least 4 then the AI will cast them all on itself and have no energy regeneration (or even negative if you have more than 4). Divine Boon will cost them extra energy when they heal, when they run out of enery they will stop healing and have no benefit. Life Attunement will make them deal less damage and since they can not heal due to lack of energy they get no benefit. Blessed Aura is good too since they can not cast enchantments anyway. Holy Veil is good if you donâ€™t plan to use hexes.

Necromancer Tips:

 * Equip hexes such as Malign Intervention which take time and energy to cast but which won't accomplish anything useful in the one-on-one fight. The AI will waste time and energy casting them on you.
 * Bring spells which require a health sacrifice: the less useful in the one-on-one fight, the better. The AI will reportedly waste its own health casting these.  For a necro warrior, equip a sword and shield.  The doppelganger will have an axe and bow.  You will have a distinct armor bias. Also, Dark Pact can work nicely.

Ranger Tips:

 * Bring slow-casting Nature Rituals like Winter and Quickening Zephyr: the less useful in the one-on-one fight, the better. The AI will waste time casting them while you apply the beatdown.
 * Bring traps. Cast them at the beginning of the fight while the Doppelganger is busy casting them himself, then run back. The Doppelganger will follow you in a straight line and is not smart enough to avoid your traps.

Warrior Tips:

 * Equip Frenzy but don't use it. The AI will use it, putting itself at a significant disadvantage in the one-on-one fight.
 * Bringing Hammer Mastery or Swordsmanship skills exclusively does not work. Despite wielding an axe, the Doppelganger will be able to use those skill nonetheless.