If you can make it to Level 20 / 30 / 40 / 50 without dying once along the way, a secret door will appear. The Secret Rooms found in Level 20, 30 and 40 contain large amounts of bonus items as well as a Secret Encoded Message on the lower half of the screen. The first line of the secret message is THE ALPHABET (ABCDE...) that you must use to decode the message. The code is the same for every room & will be needed to decode the secret message at the end of the game (to open up Super Bubble Bobble). You may want to take a screenshot of these rooms so you can decode the secret messages later as the game may force you to proceed through the game. The Secret Door in level 50 is actually a 20-level warp, taking you directly to level 70.