From Destinypedia, the Destiny wiki
In the Arkborn and Mockery encounters, these Ogres are to be killed to progress through the encounter and to gather points required to arrive at the boss. In the Riposte, they are the final boss, where they are to be killed by Cleavers and gunfire following the depletion of the shield. These Ogres can quickly sunder a Guardian's health, as well as absorb a significant amount of punishment.
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