From Destinypedia, the Destiny wiki
Gahlran's Deception appears as a large, half Cabal/half Hive enemy. He is surrounded by a shield that is only penetrable at point blank range, and wields two very large blades. He grunts loudly when he lunges at a Guardian.
Once a Deception is punched, the fakes will dissipate and the real one will begin engaging the Guardians stuck within its segment. The side with the real Deception will be the last group to be blessed by the team. The side to the right of the Deception will get the Blessing first; one person should pick it up so both members can kill the adds that spawn. The third wave will contain a group of blessed only enemies, including an Ogre. Once the wave is killed, the side should head to the active vessel (clockwise to the right) and swap the buff with an ally while one person on the other side gets the Blessing and the wall between the sides breaks down. This is to be repeated until the last wall is broken, and the Deception attempts to cast a Hive Annihilation Ritual. To deny this and begin damage, a blessed and non-blessed player should melee the Deception at the same time, which will break the dome shield and stun the Deception. Only non-blessed players can damage the Deception and blessed players attacking the Deception or those caught in the bubble when the melee is done will lose the blessing. Damage is to be done until damage phase is done or the Deception falls.
During the Gahlran fight, Gahlran will create Deceptions in a clockwise order. They are to be killed before they cast the Hive Annihilation Ritual, and to do so, the blessed and non-blessed players must stun the Deception in front of Gahlran. The team should wait for Gahlran to fire his Incendiary Rune and shoot the green hand once it's all finished. Then Gahlran will recoil and slam the ground with a massive Cleaver, which will hopefully catch the Deception in the blast and kill it.
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