OK so here are my thoughts. We can see elements: poison, ice, fire and water. If you look up, when the poison appear, it looks like there is a portal to a swamp like area, a snow type area when the ice appear, and a volcano type area when the fire appear: broodmother, megapithecus and dragon arena. So we are inside the obelisk and the water element leads to another boss which I assume will be a water boss. The blue portal when the water appear may be the surface of the water seen from under.
(Excuse my english, not a native speaker)