Press L2, R2, L2, R2, Square, Square, Circle, Circle at the main menu. You'll hear a sound if you did it correctly.
All power moves and 120 achievement points:
Press L1, L1, R2, R2, L2, R2, L1, R2 at the main menu.You'll hear a sound if you did it correctly.
Press Square, Circle, Square, Circle, L2, R2(2), L2 at the main menu. You'll hear a sound if you did it correctly.
Press Circle, Square, Circle, Square, L1, R1, L2, R2 at the main menu. You'll hear a sound if you did it correctly.
Unlimited Electric Batarangs:
Press L1, R1, L2, R2 at the main menu. You'll hear a sound if you did it correctly.
All Weapons and Unlimited Ammo:
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 unlimited ammunition.
The Secret Envelop:
On Level 4: Rooftop Battle when you go inside the door on the balcony and come out the other door which leads to another balcony Instead of using the Batgrapple to launch across the chasm, drop off of the balcony and onto the roof. Just a little jump will work fine. Turn to the left past the gated tree area and walk to the edge. Walk off the ledge and land on the narrow ledge below. Walk along this ledge to the left corner and head around. Use the Batgrapple to pull yourself up to the small balcony and open the door. On the floor, just inside the room, is SECRET ENVELOPE A. Pick it up and head out the other door. After you beat the game you can use this envelope refill your ammo.
Secret Envelope B:
On the Bridge Level 1 after you defeat the first goon you will notice a yellow flashing object on the top of the boxes. You probably have already tried to get onto the barrels and glide onto it finding out that you cannot do that. What you must do is go to the ladder turn around and jump/glide to the little platform to the right of the boxes. Once on the platform glide to the next platform where the object is...congratulations, you have just earned Envelope B. (hint: this will take a few tries so be patient)
Secret Envelope D:
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 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 eight boxes and pick up Envelope D. (hint: this is a very frustrating cheat and you WILL NOT get it on the first try)
Secret Envelope E:
Go to 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 at the correct time jump into 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 this door and inside is Envelope E.
Thanks to Revolution readers Dick Grayson, Specter, Tomas Yates, Qbbatman and Lars Johnston!