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.