He will call for secondary colors , like "orange", after a while & become immune. You need to bring the mob to the 2 colors that make orange (hint : red & yellow) and his immune buff will fade after a while. When it does, 2 adds will spawn & you can dps it again.
There is a puzzle involving the blocks to fill the chamber with water, no solution here so far.
Once the named is pulled a LARGE bubble will form. Drag the named into the large bubble. About every 25% the bubble will pop and a new bubble will form (I believe it was in a clockwise order). Move to the next bubble, rinse, and repeat.