Prismatic Taken Captain
From Destinypedia, the Destiny wiki
Prismatic Taken Captains are rarely appearing Taken Captains seen in the European Aerial Zone, where they usually spawn during the boss encounter in the activity. Indicated by a Public Event icon on the HUD, the Taken Captain will spawn somewhere on the map, giving players an optional chance to increase their combat efficiency with the Elemental Orbs they drop.
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