go to the level "an enterprising theft" then when your in the room where toxic fills the room. Become sonic bat-man(must be in free play)bust open the door (where the janitor is)then be Mr.freeze keep freezing him. He will never die so you will get "free easy money"
This isn't a cheat but when you are at the batcave (where you can change suits) make sure to have Robin's DECOY move with his Tech suit. Then press O and switch to that Robin. (this also works for NightWing) Move away from the real Robin and for you to die and BAM you have a new Robin. (I did this and got over five Robins lets see if you can get more)
These two characters are unlocked when you beat the game with the corresponding task completed.
Unlock Hush: Rescue ALL 25 civilians in the game. To find out which levels you still need to rescue a civilian look for the small face with either a happy or sad face indicating whether or not you still need to rescue them.
Unlock Ras Al Ghul: This villain whose name means 'The Demon's Head' is unlocked when you have collected ALL 300 of the mini kits. There are 10 in each of the 30 levels.
To unlock Arkham (psychiatric hospital for the criminally insane) you must achieve 'True Villain' status on ALL levels in the Villain storyline by collecting enough studs to max out your stud counter on each level. To access the villains and the level go to the right of the Batcomputer and down the ramp and pull the lever. Then go through the door on the right to reach the Memorabilia room where you then climb the ladder at the top.
To unlock Wayne Manor you must achieve 'Super-Hero' status on each of the Hero missions or alternatively achieve 'Super-Villain' status on each Villain mission. To reach these statuses you have to collect enough studs to max out your stud counter on each level. To access the mission go to where the vehicles are in the Batcave and then go to the far right and down to the bottom. Step on the elevator which will take you to the Memorabilia room and the Wayne Manor mission is in the upper left corner.