From Destinypedia, the Destiny wiki
The Gravetide Ogre will spawn only after killing the Wizards next to the Gravetide Summoner. It will continuously fire high damage eye blasts at the player. The player will need to damage the Gravetide Ogre while also clearing the adds, consisting of Arc shielded Knights, normal and cursed, and undead Thrall. Occasionally, the player will earn a buff in which they can harm the boss with more damage. On a third of health, the Gravetide Summoner will attack the player. When the Ogre is dead, the Wizard will be vulnerable to attacks.
List of appearances