First, a word on the personal computer conversions of the game. I have played versions on the IBM PC, Commodore 64 and Amiga, and none of them come close to the same atmosphere and playability of the original coin-op. Although the levels and monsters are pretty much the same, the gameplay is different, and many of the cheats and hidden features are missing. That is not to say they are poorly coded games, considering the hardware they were designed to run on, but if you haven't played the real thing, you don't know what you're missing!
Anyway, most of my knowledge is of the original coinop version of BB.
In the background of each of the treasure rooms, a secret message is enscribed in a weird character set. The messages can be decoded once you realise that the first 26 characters are the 26 letters of the alphabet. The messages are: (spelling and grammar are as they appear in the game!)
If you make it to level 50 without losing a life a magic doorway appears that warps you to level 70. The magic door on level 50 appears VERY VERY briefly in the middle of the level, if at all. Just head straight for the spot in the centre of the screen and don't kill any monsters.
The "original game" cheat (see below) causes the treasure room and warp doorways to appear regardless of how many lives have been lost.
There is one version of Bubble Bobble I have seen that did not follow this rule, but the only letters that ever appeared were red E's!! Must have been a buggy version.
If there is only one player left when you complete level 100, you get a message about never forgetting your friend, and are sent back to a random level. This allows for extra long games, and you can "make a profit" on lives by earning more extras before you get sent back again :) The only way to complete the game is to complete level 100 with both players still alive. Some of the rarer items in the game are more common after you have been sent back. Usually, within one or two levels of being "sent back", a Treasure Chest will appear.
There are two extras before 500,000 (there is a choice of 4 dip switch settings for the exact point value for them), an extra at 500,000 points and one for every million up to 5,000,000. As far as I know, there are no more extra lives from score after 5,000,000 points. My record is 8,800,000.
Left, Jump, Left, 1P, Left, Fire, Left, 1P.
The message, "POWER UP!" appears at the bottom of the screen. This gives you
Speed, quickfire and rapidfire bubbles permenantly throughout the game.
Fire, Jump, Fire, Jump, Fire, Jump, Right, 1P.
The message, "ORIGINAL GAME" appears at the bottom of the screen. This makes
the magic doors to the treasure rooms on levels 20, 30 and 40 always appear,
and the warp to level 70 on level 50 most of the time. Without this cheat
they only appear if at least one player has made it to those levels without
losing a life since the start of the game.
1P, Jump, Bubble, Left, Right, Jump, 1P, Right
The word "Super" appears in the Bubble Bobble logo, and the monsters change
in the demo levels.
Hints for this cheat are hidden in the game in a classic way. Each treasure room has an encoded message in a weird character set. To decode the message you need to work out the relationship between the characters and the letters of the alphapet. Luckily, the first 26 characters are the letters of the alphabet in order. I had to take a photograph of the screen to work this out! The messages, once you decode them, do not mean anything useful, but when you complete level 100, there is another message in that character set which tells you the Super Bubble Bobble cheat.
If you complete Bubble Bobble in normal mode, you get "But it is not a true ending...", and a cryptic clue on how to get to treasure rooms so you can decode the message. Completing Super Bubble Bobble gives you the True Ending.
"Super Bubble Bobble" mode is actually an option which can be set permenantly with a dip switch on some machines, in which case this cheat is useless.
Since you exit the treasure room when you die, you must have only one life left when you enter, and thus this cheat is only possible if you are using the "Original Game" cheat.
The water sloshes back and forth for eternity, and the level never ends because there is infinite time and the last monster never leaves it. Once the other monsters are killed, there is no way to die, so the only way out is to switch the machine off! This Move could be used by unscrupulous players to gain a free credit in an arcade by claiming the machine had crashed :-)
Another interesting feature of the previous screenshot is the ownerless paddle
bouncing back and forth at the bottom. This can happen if you kill a monster
at just the right time. It is still just as deadly, so in fact in this
particular case there is a way to end the game.
Another way to rescue your friend if they have just died is to get the last letter to spell EXTEND while they are still spinning around in agony. They will not lose a life if you jump to the EXTEND screen in time!
Armour - Well, it looks like a little suit of armour, anyway. After picking this up, a warning red flash and bell sound at the beginning of a level indicates that a special destructive magic item will appear somewhere on that level.
Flashing Bubble - Extremely rare; a good omen! A red, pulsating bubble which floats up from the bottom of the level. Popping it is worth 100,000 points and gives fireballs to the player that pops it for the next 5 levels!
Treasure Box - Behaves like a candy stick, ie after the last bubble is popped, all the bubbles turn to bonuses and a large bonus drops into the middle. However, with the Treasure Box, the bonuses are diamonds, and the large bonus is worth 50,000 - 80,000 points!
Bracelet - Causes stars to rain down, killing all monsters in their path, and giving lots of points to the person that picked it up. There are other similar items, such as the pitchfork.
Clock - Behaves differently on different Bubble Bobble implementations. On some, it freezes all monsters in place, while you can move around and bubble them. On others it gives you infinite time on that level (Baron von Blubba never comes to get you).
Skull - Not a good thing to pick up. Probably the only bad item in the game! All it does is cause the "Hurry Up" message to come straight away, and the monsters go red and speed up.
Potion - The monsters disappear, and bonus fills the room. Get it all and an extra 100,000 points is yours. Great fun in two-player mode, as the extra bonus is only 50,000 for the player who picked up the least. Both players can get 100,000 if they cooperate and get the same number of bonuses, but that is not always possible.
Is there a cheat you can do after completing the game? I remember seeing some guys who would always try to hold down all the buttons after completing the game, but I have never had any reproducable results. Occasionally, the game becomes confused and a new game begins while the ending credits are still scrolling over the top! Then the machine crashes. I've never worked out how to reproduce this exactly.
Do the messages in the treasure rooms actually mean anything, or are they just to help you work out the code?
Are there any hints in the game as to how to perform the Power Up and Original Game cheats? I have never seen any, and just got them from other players.