Cheat mode
 At the main menu, press L, R, L, R, X(2), Y(2). If you entered the 
 code correctly, you will hear a sound.
 
 
 Infinite batarangs and electric batarangs
 At the main menu, press L, R, B, White, L. If you entered the code 
 correctly, you will hear a sound.
 
 
 Bonus characters
 Press Left, Right, Down, White, L + R, then press Start at the main menu.

 
 Envelope A
 Go to the Rooftop Battle level. When the clowns chase Mary, you 
 will go up to the rooftops. Grapple hook up to her roof and beat 
 up the white clown. Go up to the next roof, where you are on a little 
 balcony. Jump across, then go in to see a thug run across a hall 
 with the girl. Follow and he will jump off the roof. Follow, look 
 down, and drop to lowest edge. Walk along to left until at the corner 
 the grapple icon appears Grapple over, go in the door and pick up 
 Envelope A.
 
 
 Envelope B
 Go to the Bridge level. Knock out the thug at the start of the level. 
 You should see the glowing item on the left when you start. Climb 
 the ladder and jump/glide around the crate onto the other crate. 
 Then, glide onto the platform with the letter.
 
 
 Envelope C
 Go to the Plant Electrocution 2 level. You will start the Plant 
 Electrocution 2 level by sliding down towards some holes in the 
 ground. The second hole is not fatal. Fall into it and glide (to 
 avoid minor damage). You will see a lit area. Glide down there and 
 pick up the item you find inside. Use the grapnel to exit, jump 
 out of the hole, and finish the slide. The item you picked up should 
 be the key do the door right beside the vines behind the glass. 
 Go inside and fight one of the "Plant Men". You will find an envelope 
 that has a "C" on it in the room. When you finish the game, you 
 can activate this cheat for all weapons and infinite ammunition.
 
 
 Envelope D
 Go to the SWAT Chase level. You will enter the elevator shaft. Ride 
 the elevator all the way down until it stops. Get off the elevator 
 and wait for it to rise again. After it rises, jump down to the 
 bottom and use first person mode to find the control box. Use a 
 Batarang to disable it and the door behind it will open. Stay clear 
 of the elevator and wait for the correct time to get in the open 
 room. Inside the room is "Secret Key 2." Get out of the room and 
 ride the elevator up to the top. At the top there is a door that 
 is supposed to be locked. The key opens the door, and inside is 
 an envelope with the letter "D" on it. Finish the game and the cheat 
 will be unlocked.
 
 
 
 Envelope E
 Go to the Gasworks level. You will reach a room with two levels, 
 each floor with two goons on them. First, take out the goons. Then, 
 look around on the lower floor until you see a sewer pipe with boxes 
 in the sewage. Carefully glide down and land on the first box. Jump 
 over the next few boxes and pick up the envelope with an "E" on 
 it. Finish the game and the cheat will be unlocked.