The Arkham games are full of water egg and references, tell me about your favorite(s)!

I love all the easter eggs and references Rocksteady (and WB Montreal) have put in their games. So many good to choose from, from small insane details to way bigger things. I personally love this easter egg from Arkham Knights DLC: A Matter of Family, where you can find Starro in a tank, in the theme park Joker had taken over. It really expands the Arkhamverse in a crazy way to me.

But tell me about your favorites. Big or small.