Just have two or three people with HMG kill the taken floating eye looking things for a buff. They let you do more damage to the ogre and you can have a max of three stacks so kill three then focus the ogre. Kill another eye thing before the buff timer goes away and it will reset. Have anybody else kill adds (there's ogres on the sides) or shoot the main ogre when possible. Once the Ogre is dead kill the wizard, who is the boss, fast or another ogre spawns. Wizard death=success