Riddle Solved

"Batman!" he said--and then his mouth snapped shut. His eyes went wide. After a moment, it opened again, and he said, "I flee sky and earth alike, and all things green long for the touch of my tears."

A riddle.

"Clouds," Batman said.

"Very quick!" the Riddler said.

Batman: Arkham Knight: Riddler's Gambit, Chapter 25, Pg. 265