I started playing this on 31st October last year, just so I could get "I'm Batman" to pop on Halloween! Then I quickly saved Catwoman for the "Acid Bath" to unlock. Finally I spoke to Calendar Man, got the Halloween date marked off, ran out of the courthouse and saved, while only playing the game over THE PAST YEAR simply to speak to him.
I'm now 2 weeks away from popping the achievement, which will come up on my games list as the third achievement unlocked, cuz that's how I roll.
THEN I CAN FINALLY PLAY THE FUCKING GAME!!!!!!!
And I still have never heard any spoilers