Danny wouldn't say that the ghosts were cheating to visit the human world because technically they weren't, they were just hiding in plain sight, using the portals near or within the sea.
None of them needed to breathe and hardly anyone questioned the glowing things that appeared in the sea anyway. Of course, he didn't think he'd find a whole underwater city down there, with a government and a king, but thanks to invisibility he was sure they hadn't noticed them.
Well, he was almost sure, because a bat-shaped yacht was cruising the docks and the Atlanteans were strangely on guard. Danny wondered what was wrong with them.
Of course, Bruce and Arthur were investigating the sudden increase of toxins in the sea. Many locals (Atlanteans and Gothamites) had claimed to see something constantly glowing green floating near the shore, too far away to confirm what it was, and both feared it was Kryptonite.