Remember : rooms with a piston lie, the inscription on the room where Robin is tells the truth, the other inscriptions can equally be right or wrong. Knowing the problem itself is insolvable, and knowing that the answer to "is room #8 compartment empty ?" allows to find Robin, where is he ?

 

This Riddle is a lot easier than it seems. Don't bother to study every case, there are too many. To go across a maze, you first need to find its entrance : if you look closely, inscription #8 is the only one that's not mentioned by others. So, you must first find what its compartment contains.

 

Does inscription #8 tell the truth ? It says "I kill and #9 is empty", so it can't be true, because it says that it kills, which - if true - would mean that it contains a piston, which would imply that it lies : that's a contradiction, therefore, it lies and contains a piston or is empty. Since it lies, either it doesn't kill (meaning it's empty), either compartment #9 isn't empty, or both.

If compartment #8 were empty, we couldn't logically decide whether the second part of the sentence, "#9 is empty", is right or not. That would mean that the Riddle would be insolvable, and this is why Batman asked if compartment #8 was empty. But, I replied that the maze could be solved if I answered Batman's question, so that means pillar #8 contains a piston.

 

As it contains a piston, the part "I kill" on the inscription is right, so the second part, "#9 is empty", has to be wrong since the whole sentence is wrong. So, pillar #9 compartment isn't empty, it contains Robin or a piston, and you can now by yourself wander into the maze and find Robin...

Good luck !