You can stay all the way up at the top with a sniper rifle if you want. Just kill the adds on the left or right if the boss is getting shielded that way the golbins will cycle through to each side instead of shielding him.
Either way, good luck!
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Did the same, stay around the area where the first oracle spawn in the raid mode. When the boss has a green energy field it will be immune just shoot the goblin to break the bond or wait till it switch side right to left, left to right. When the boss has an clear invisible cloaking is when it can take damage.