"A natural cure for Scarecrow's doom, your savior's gone, but still in bloom."
This riddle can only be solved after Poison Ivy's death. Return to the Botanical Gardens and check the spot where she passed to find a small flower blooming, and scan it.
"Disarming, charming, quite the inquisitor. She'll pull back the vale, whoever her visitor."
There's a large neon sign for the Vicki Vale Show near Grand Avenue. Get on a rooftop for a clear view, then scan it to solve.
"The League of Assassins stuck blades through hearts, now they impale each other's art."
There's a large parking garage in Kingston. Check the lot by the entrance to find this Demon's Head poster skewered to the wall with a sword. Scan it to solve.
"Are you suffering from a mental split? Take out the trash before you defend it!"
You'll find Hell's Gate right across the street from the Botanical Gardens. Scan it to solve this riddle.
"You forced this contraption over my brain, I'll reward you with punishment, debasement, and pain."
Found inside Pinkney Orphanage, inside the final Riddler/Catwoman room. There's a console by the puzzle you can activate with the Remote Hacking Device. This opens up a small hidden room. Scan the helmet inside to solve.