Exploring the secret depths of Bubble Bobble's design
Secrets can tell you a lot about how a game was designed, and Taito's classic Bubble Bobble is full of them.
Today we're off on a trip to visit one of the least-seen, a secret room that shows up if you get to level 20 without dying. I've been there several times, and I'll show you how you can reach it too, and fairly! But I'm getting ahead of myself, let's introduce the game first….
Taito's popular 1986 arcade game Bubble Bobble is one of a class of game that we might call SRPPs: Single Room Platformer-Puzzle games. These are a category of game that consists of a series of single side-view rooms, where the player controls some small surrogate on the screen, and must typically use a basic set of abilities, often just jumping and a means of attacking, to defeat all of the enemies in the playfield-like room, which then allows passage to the next room, among some large number of them.
Although Donkey Kong itself fits the description if taken literally, SRPPs are actually a fairly exclusive genre. Taito made a few of them, some of them sequels to Bubble Bobble itself; others of the same type are Bubble Bobble's predecessor Chak'n Pop, contemporary The Fairyland Story and Toaplan's 1990 release Snow Bros.
Of them all, Bubble Bobble is the best known, so popular as to be almost legendary. Its popularity is a result of its shallow difficulty curve, its insanely catchy music, its easy-to-grasp gameplay, its vast number of power-up items, and the game's ridiculous depths as far as secrets go.
One of the secrets is the purpose behind this article: there are a set of three secret rooms that become available to players (up to two can play at once) if they can reach rounds 20, 30 and 40 (out of 100) without losing a life.
These rooms are (assuming you weren't spoiled) one of the keys to finding the game's "true" and "Happy End" ending, for reasons we'll get into, but reaching even level 20 without dying at all is quite challenging. This guide is here to help you achieve this feat on your own, and understand how the dev team's decision to implement these secrets adds a new dimension to the game's design.
The Bubble Bobble series
In addition to the original game, there are at least three intersecting and crossed-over series connected with Bubble Bobble that interested devs and players might wish to examine. There's the original sequence themselves, which could be taken to include Rainbow Islands (arcade and ports) and Parasol Stars (various console and microcomputer versions, but no arcade release). Bubble Bobble might also be seen to be a follow-up to the earlier arcade game Chak'n Pop. All of these games are SSRP-type games (except maybe Rainbow Islands), although some of them have some amount of scrolling within their rooms.
Even if they're in a similar genre, these games still play differently enough to Bubble Bobble that there was demand for more games with Bubble Bobble's specific play mechanics. That would bring us the rare Famicom/NES game Bubble Bobble Part 2 (1993) and arcade games Bubble Symphony and Bubble Memories.
On top of these, there's also the Puzzle Bobble side-series, also known as Bust-A-Move, which have completely different play style but use many of the same characters.
Bubble Bobble basics
The game consists of 100 rooms of enemies that can be tackled either by one player going solo, or two playing cooperatively. Each room has different enemies and a different layout. Every room is a single screen. While the game is a platformer, unlike most of them, a player character falling off the screen doesn't immediately lose a life, but instead wraps around to the top. It's very easy to die in Bubble Bobble, so even small advantages should be appreciated.
The player's representatives in the game world are "bubble dragons," color-coded green or blue depending on player. A bubble dragon's a cute li'l lump of scales that can jump about four blocks high (blocks here are much smaller than those in Mario, mind you), with very little control over your motion when you're in the air. You can adjust your motion slightly while in mid-air, but there's still not much you can do once you've launched yourself.
Zen-Chan (aka "Bubble Buster")
Walks left and right, jumps straight up, sometimes takes a running jump to the side.
Moves diagonally, bouncing off of solid objects. Fairly predictable.
Moves as Zen-Chan, but also fires large, round rocks at players on the same line.
Flies left and right quickly, while slowly moving up or down. A little harder to handle than Monsta.
A lot of deaths come from when you take a leap, and an enemy hits you before you land. In fact, a lot of deaths happen, period. Our favored soaplizards are fragile like, well, bubbles. If any enemy so much as brushes against one of them, they perish on the spot. Bubble Bobble is not sparse with extra lives, at least at first, but it's not long where you're losing them all over the place, and then the game is over.
Continues are odd—you are free to join or continue a game at any time so long as the other player is still playing. If you're in a single-player game, then your game ends the moment you lose your last life, but in a two-player game continuing is easy so long as both players don't run out of lives at once. Unlike as you might be expecting, adding another credit does not allow a running player to simply buy extra lives. This adds a bit of strategy; to get far, the players must be desperate not to run out of lives at the same time. It can help to keep credits in the machine for the event that one player fails early; then they can at least pound on the start button to try to rejoin before their partner also fails out.
It's not just enemies that are problems for our reptile heroes. Bubble Bubble's levels have some places where, if a player enters them, it is basically impossible to escape. One of the earliest such places is Level 19, which has a number of tall shafts with ground at the bottom, far too far for a player dinosaur to leap from. There are a lot of these places where a player can get out by blowing bubbles then jumping on them, holding the jump button down and thus bouncing on them over and over. If that's not possible (the case if the shaft is two blocks wide, as the bubbles have nowhere to go), sometimes a player can get out by popping a passing Water Bubble, letting the flow carry them out of the trap.
If none of these options will suffice, the player must either try to somehow defeat the remaining enemies from their trap (usually using passing elemental bubbles) or wait for the Skel. The Skel, aka "Skel Monsta," aka "Baron Von Blubba," is a skeletal white whale that appears if the players take too long to complete a level. It is an example of what I call a baiter, after Defender's harassing enemy, a powerful, sometimes invulnerable, foe that arrives if the player stalls the game for too long. The Skel is easy to avoid if the player has full movement, at least at first, but it homes in on the players faster and faster until it kills one of them. In a two player game each gets their own Skel. At least, in the process of losing a life, the player is freed from their trap.
However, this is not acceptable for us on our audacious quest. For we are bubble dragons on a mission: to lay our eyes on one of the game's fabled Secret Rounds, and behold for ourselves the wonders contained therein.
Secrets upon secrets
Bubble Bobble's reputation is not built off of its easy-to-grasp gameplay alone. A lot of it, maybe most, comes from the insane array of awesome items and secrets buried in the game. Bubble Bobble's cute facade hides a true player's game, an experience that must be studied and practiced to master, and even then, there's a lot of studying and practicing to do.
About those items. It's usually not far into Bubble Bobble (maybe as early as the first level) where one of the game's many entertaining special items show up. There's the Blue Cross, for instance, which immediately floods the whole board with water and instantly defeats all the enemies, turning them into valuable diamonds. The various Cane items create a gigantic, high-scoring bonus item that appears in the center of the board once the last enemy has been defeated.
Then there are three different flavors of candy, each of which provides a useful powerup that lasts for the rest of the current life. There's powerful weapons, invincibility hearts, time stop clocks, bonus rounds and many other wonderful prizes to discover. There's even an item (the Bell) that alerts you if other powerful items are due to arrive soon. The best of them all may be the Umbrella, which outright skips you forward from three to seven levels.
These special items are quite powerful, and Bubble Bobble is hard enough that figuring them out is an important step towards learning to play it well. We'll be getting to that shortly, but in the meantime I should explain what the Secret Rounds are.
When you reach levels 20, 30 and 40, if at least one player in the game managed to get there without losing a life, its entrance is actually presented as one of these secret items; it just has the graphics of a silver doorway instead of some random treasure. If a player manages to make it to level 50 without dying, the prize is a golden door that skips 20 levels, but good luck finding that one.
First things first. If you're playing this in an emulator, go into the machine settings and set it to Easy. There's no reason to make this harder than it has to be. Bubble Bobble has a dynamic difficulty feature that increases the difficulty when you gain a life, and decreases it when you die, that can play a major role in your progress. This means, even if you start the game on Easy settings, after a while it'll creep up towards high difficulty anyway. High dynamic game difficulty both increases enemy speed and reduces the time enemies stay trapped in bubbles before breaking out.
Since your aim is to get as far as you can without dying, this means it's actually a good idea to avoid extra lives. These have two sources: points and EXTEND bubbles. If you're serious about getting there by any means, you might want to disable extra lives by points in operator settings.
The first few rounds are easy, especially in an arcade where you're very likely to find powerful items in the first few levels. On a freshly initialized MAME setup this never happens, but in the meantime you'll have to clear these boring early boards yourself. Take advantage of the downtime by launching a lot of unnecessary bubbles and jumping a lot. Why? Well....
Nearly every round in Bubble Bobble generates two items, a points item that appears first (usually 7 seconds in), the value of which depends on how long it took you to finish the previous level, and a special item (at 12 seconds) that give you some kind of ability. There's a tremendous variety of these, and they give Bubble Bobble a lot of its appeal. What's not well-known is the fact that, despite appearances, they aren't random at all.
Every special item has a trigger condition, something you've done in the game up to that point that makes it appear. Internally, Bubble Bobble maintains a large array of counters, and is constantly watching, recording everything you do in a game like a Z80-powered NSA agent. At the start of every level, the game looks through its list and stops when it finds the first counter that's exceeded a specific target value. This target value is usually unchanging, but for some items depends on the game's operator-set difficulty level.
When the machine finds a count that's gone over its threshold, it resets that counter to zero and sets a specific special item to appear on that level. It only does this once per level; any other counters that have been passed continue to grow. There is a set order in which the threshold values are checked, usually prioritizing the more exotic and powerful items, whose triggers are difficult to activate. It also does this regardless of whether the item actually appears or not; if you finish the level before it shows up, it's lost.
The thing about all those counters is, they are not reset at the start of a game! Any progress the previous game made towards generating special items is retained, meaning successive games can take advantage of them to improving their own state. This is what makes playing via MAME a bit more boring than on a physical arcade machine; when an emulated MAME machine starts up, all the counters are initialized at zero, meaning that the first level, instead of possibly generating an awesome item like a Lamp or an Umbrella, will see no special item generated at all!
(As a personal aside, I love it when communal game systems like arcade machines use the actions of past games to influence succeeding ones. Usually, one expects a video game to begin from a zero state every time it is played, but this isn't always the case! Pinball machines sometimes have what are called progressive jackpots that make this kind of thing more visible.)
But one thing that is true of an initialized MAME game is that the Candy and Shoe items, which provide basic but life-lasting powers like rapid fire, fast bubbles, long range and quick movement, but which appear late in the threshold list and this often get overruled by flashy yet temporary powers, have a better chance of showing up. You can trigger them yourself, and should take advantage of the early rounds by building them up. Pink Candy (long range) appear after players fire 51 bubbles; Orange Candy (rapid fire) appears after players jump 51 times; Blue Candy (fast shots) appears after players directly pop 51 bubbles; and the fast-movement Shoe counts the number of frames that players have collectively spent moving along the ground. If you're efficient about building up your counters, you can have all four of these powers active by the end of Round 5.
Pink Candy: Long Range
Triggers when you fire 51 bubbles
Orange Candy: Rapid Fire
Triggers when you jump 51 times
Blue Candy: Fast Shot
Triggers when you pop 51 bubbles
Shoe: Extra Speed
Triggers when you run a sufficient distance on the ground
There are two other items of special interest to us. The Magic Potion items, when collected, immediately cease the current round and turn it into a bonus round, filled with points to collect, but more importantly immediately defeat all the enemies upon collecting it.
There's a number of other items that instantly finish a round for us, but most of them have special requirements, like popping a lot of Fire bubbles, collecting a lot of items or killing enemies with different elemental bubbles. Potions are special because their requirement can be done on many levels.
Their trigger counter follows the number of times either player wraps around the screen from bottom to top. Do this at least 15 times and a potion will appear in an upcoming round. You can do this quickly by finding a place where a bubble floats near the top of the screen and bouncing on it repeatedly, causing your lizard-guy to bounce up off-screen, or else finding one of the rare levels where there's a step from which you can naturally jump high enough to wrap the screen.
Of even greater importance are the Umbrella items. These items instantly advance you ahead up to seven levels, and you still get credit for the levels you passed as if you cleared them. If you could somehow make Umbrellas appear at will the Secret Rounds would be easy to reach, but their appearance is limited by the fact that their trigger condition counts popped Water Bubbles, which do not appear in most rounds, and appear slowly when they do. 15 Water Bubbles popped (whether they release water or not) will cause the weakest Umbrella, that skips three levels, to appear.
To get the five-level skip Umbrella, you must have a total of 20 Water Bubbles popped at the start of a level; to get the most valuable, seven-level-skip Umbrella, you have to have popped 25 of them. You'll be lucky to see much more than 25 Water Bubbles appear in the first 20 rounds, so you'll probably only be able to trigger one Umbrella in that time. Fortunately, the first two Water Bubble rounds are fairly easy, and with careful play you can pop many of them before the Hurry Up alert appears.
Cane: Makes a giant bonus item appear at end of round
Triggers when you pop 3 of the same EXTEND bubble
Potion: Immediately begins a bonus round
Triggers by wrapping around the screen from bottom to top enough times
Cross: Grants a special attack power
Various triggering conditions
Umbrella: Skips next 3, 5 or 7 rounds
Pop 15, 20 or 25 Water Bubbles
Ring: Grant all candy powers & bonus points for rest of round
Triggers when you eat three of the same candy
All of that said, here are the first 20 rounds of Bubble Bobble, and how to conquer them, hopefully on the first life:
#1: Difficulty: *
Befitting the first level of such a long game, this one's a breeze. Not only are there only three weak, slow Zen-Chan enemies to deal with, but trapped enemies won't start to escape until nearly the Hurry Up timer. Take advantage of this by blowing a lot of bubbles and popping them, while jumping a lot, to set up Candy items in upcoming rounds.
#2: Difficulty: *
Just one more enemy here than last time. Jump up to the center ledge and bubble the Zen-Chans as they come down. With practice, you can get them all before they fall down further, but if you miss one or two it's not hard to track them down. After they're all bubbled, you can use the rest of the time preparing more Candy, or doing laps back and forth on the bottom level to prime a Shoe powerup.
#3: Difficulty: *
The first thing to do is to immediately jump up to the point to the left of the READY! in the screenshot, and keep firing bubbles to the right until all enemies are encased. Remember, if you clear a level before a special power item appears, you lose it, and if you defeat the last enemy in a level, any special item left uncollected will immediately disappear. Make sure to wait at least 12 seconds to get the item!
#4: Difficulty: *
Jump up to the ledge above you and bubble the Zen-Chans as they fall into range, just like in Round 3. You'll probably start seeing EXTEND bubbles here, which are generated when you pop three or more enemy bubbles at the same time, carried over from previous rounds. Spelling EXTEND will instantly clear the current level, which is good, but also award you an extra life and thus increase the difficulty, which is bad. Still, I usually just go for the letters anyway, because it's fun.
#5: Difficulty: **
This is the first level with Water Bubbles. Try to bubble the four Zen-Chans then hold out on popping the Water Bubbles until Hurry Up begins. Be careful though, the Zen-Chans will probably escape before then and have to be rebubbled. The air currents in this level also tend to draw their bubbles to the top of the screen, where they'll get mixed up with the Water Bubbles. If you end up killing the last enemy by accident don't feel too bad about it, as it frequently happens.
#6: Difficulty: **
This level is similar to the previous one, but two of the Zen-Chans have been replaced by Mightas, which have projectile weapons. Be careful any time you're in a horizontal line with them. It's still early in the game so they'll be slow, but still, bubble them quickly. It's a lot easier to farm Water Bubbles here, and it's possible to get up to 15 popped total by now, but it's best if you stop at 13 or 14, so as to have the best chance of getting a seven-level Umbrella later.
#7: Difficulty: **
Four Mightas appear here. Use the same trick you've been using, standing on the ledge below them and bubbling them as they fall in front of you. By now you should have both long range and rapid fire, which will make it much easier. The Mightas won't stay bubbled as long before escaping, but make sure to grab the special item, which will appear in the upper-right corner, before passing this round.
#8: Difficulty: *
Now that you're decently powered up, you shouldn't have much trouble here. The worst thing about this level is that, once bubbled, the enemies won't cluster together but tend to separate into one group on each side of the screen. You've probably got most, if not all four, of the main powerups by now, and the special items will probably be boring for a few levels.
#9: Difficulty: **
Five Mightas show up. You can handle them the same way as before, but be quick! If you delay even a second, one will probably fire a rock at you. If that happens, drop down a level and try to get them there. Make sure to rebubble them if they start to escape before you pop them, which is pretty likely.
#10: Difficulty: ***
The game is now starting to heat up. Not only is this a particularly chaotic level, but it's also the first one with the bouncing purple Monsta enemies. (The game tends to introduce new enemies on round numbers that are multiples of ten.)
This is one of the levels that caused me to suggest playing on Easy difficulty; if the dynamic difficulty has gotten too high, it's easy for enemies to escape from your bubbles in just a couple of seconds. Play this one carefully. Water Bubbles show up after a short while and can help you clear out the enemies, but be cautious. Keep out of danger and pop whatever you can. It's easy to run out of time if you're too cautious, though. This level is a major stumbling block. Don't use it to farm Water Bubbles or EXTEND letters, just get through it.
#11: Difficulty: ***
At the beginning, quickly jump to the middle island then up to the center ledge. Firing left and right as quickly as you can, bubble all seven enemies as they come down.
Pop the four on the left first. You probably won't have enough time to pop the others before they escape, leaving one angry Monsta and two angry Zen-Chans on the board. The Monsta's not hard to care off: watch its bouncing pattern to predict when it'll come to your horizontal level so you can finish it off. The Zen-Chans will tend to gravitate to the bottom of the screen where they'll jump back and forth across the pits. Fall onto the middle island, on the side they aren't, then bubble and pop them from there.
#12: Difficulty: **
If you're fully powered up, and you're playing on Easy, this one can be finished quickly. Bubble all the Monstas as they rise up, from off the bottom of the screen, into your horizontal line. Then as they drift up, fall through to the top of the screen and crush them. Blowing lots of extra bubbles helps you here; when you pop a bubble, all bubbles that are close to it pop too, and so on, enabling you to pop lots at once if they're in a cluster, even if it extends far across the screen.
If you're not playing on Easy, or the dynamic difficulty has risen enough, some Monstas might escape. Try to pop any stragglers as well as you can. Do not fall into the traps in the sides of the screen unless you need to to pop the last enemy! It's very difficult to escape from them. Water Bubbles spawn on this screen, but it's usually better to go ahead and wipe out the enemies.
#13: Difficulty: **
This would be a very hard round if it weren't for the Water Bubbles that float up from the bottom. Take care of the two Monstas bouncing around outside before focusing on the ones in the heart.
There is a special trick when dealing with all the "elemental" bubbles (Water, Lightning and Fire): their effects tend to spread in the opposite direction to which you are facing. Use this to pop the Water Bubbles at the top of the heart and direct their flows into it, to kill the enemies trapped in there. Don't get swept into the heart yourself unless a really REALLY good prize appears in there, as you'll probably just get killed. Once only enemies inside the heart are left, you can try to farm Water Bubbles, directing the water away from the heart's opening but make sure to kill the last Monstas before the Skel Monsta gets you.
#14: Difficulty: ***
This one's actually not that hard if you follow these steps.
1. Take care of the Mighty that falls beside you.
2. Three Monstas will descend from above. Watch carefully so they don't land on your head, and when they get to your horizontal level dispose of them.
3. The other Mighta will attack from the right now; get it first.
4. Be patient. After a few seconds another Monsta will descend from above. Again, make sure it doesn't hit you on the head, and bubble & pop it when it's in line.
5. Finally, a single mad Monsta will be bouncing around crazily around on the screen. It won't be hard to defeat on its own, but if you've been quick, the special item will still be around, and it could be something fun like a Red Cross, allowing you to fry the last enemy with fireballs.
#15: Difficulty: **
Try to bubble all three of the enemies in the middle first, and pop them all before moving on to the top. If one escapes back into the middle room, just re-bubble and pop it. If one of their bubbles floats up and out, don't panic, just get it as best as you can.
Be careful with entering the top chamber, jumping from below. Wait for an opening then bubble them all quickly. The special item appears in the top chamber, and is sometimes a Potion. One thing you might consider doing is farming Water Bubbles, which tend to aggregate in the top-right of the screen. If you get stuck in the top before clearing the rest of the board, the flows from the Water Bubbles is your ticket out.
#16: Difficulty: **
Start out quickly, before the enemies activate, by killing the center Monsta as it falls into place, then jump onto the left-hand, single-block platform. As long as you keep shooting left, you're safe here. Bubble the Monstas as they enter range and pop them quick. Repeat for the other side when it's safe, then go up and take care of the last two trapped in the middle of the screen. There is a high chance of a good special item on this board, and it could be an Umbrella. It'd be very nice to skip the next three levels….
#17: Difficulty: **
Do it step by step. First, take care of the Monstas coming up from beneath your starting point. Try to get as many as you can from this perch. When it looks safe, fall and wrap around to the top, which is a good place to bubble remaining Monstas. Watch out for the two Mightas; the only way they can escape from the middle is by jumping straight up, so be ready for them when they do. Don't worry about the special item, appearing in the middle chambers, unless it's really good.
#18: Difficulty: ***
Be very careful here. Try to get to the top of the screen along the side. Bubble Zen-Chans, which should be moving pretty fast now, opportunistically. Water Bubbles will eventually appear and greatly help you in clearing them out, focus on survival until then.
#19: Difficulty: ****
Argh! They put this one right there, one level before your goal! It might be a good idea to save-state at the beginning and practice this one.
I should explain here a maneuver in Bubble Bobble some call the "kiss of death." It means pressing the Bubble button, when facing an enemy, at the precise moment it touches you, so that you both bubble and kill it in the same frame. If an enemy is in a locked-off chamber, this can be the only way to kill it, by jumping straight up beside it and "kissing" it as you pass by. It's actually not that hard if the enemy is still, but precise movement is necessary.
First off, you're completely safe from the Monstas in your starting chamber, but the time limit on this level is a bit short so you've got to focus on killing the many enemies here. The first thing I do is "kiss" the Monsta above while it's still in the start-of-level paralysis. Then retreat back into your starting chamber and bubble/pop Monstas that come to you. I like to stand in the low-ceiling'd opening, where you're both safe and able to blast arriving Monstas. You can care of a good number that way.
When your easy kills run out, fall straight down from the ledge, wrapping around, and land on top of one of the walls between the narrow shafts. You absolutely do not want to fall into one of those, as they are inescapable. Instead, after bubbling any remaining enemies that approach up there, leap right and fall into the wider middle shaft.
This is where you want to be, because the Lightning Bubbles that float into this level tend to gather there. You can pop them and use the horizontally-emerging lightning to kill enemies as they pass by at that elevation. The timing is tricky to master; there's about a second between popping the bubble and the lightning coming out. Remember, it always emerges going the opposite direction as you're facing! Play this one cautiously, you're almost there!
#20: Difficulty: ***
If you enter this level and haven't died yet, then the special item here will be the gate to the first Secret Round; reaching that is not only a great achievement in itself but worth over 300,000 points. It's also got pretty dang awesome music and graphics! Even if you die here, the gate will appear, but you have to get to it before it disappears.
One issue is a new enemy type is introduced here, the Pulpuls that appear in the middle of the screen. They fly like Monstas, but they move in a more gradual, wavey pattern left and right while slowly ascending or descending. In a large area like this, they're not that hard to handle. Bubble and pop them quickly. When they're out of the way you can focus on the other problem: the gate appears at the top of the screen.
There are two ways up there. The first way is to bounce on your own bubbles as they ascend the side of the screen. It's not that hard to do really: blow some bubbles so they hit the side wall, then jump on top of them while keeping the jump button held. As long as you keep holding Jump, you'll leap up off the bubble instead of falling through and popping it. As the bubble rises, you can keep rising up with it, and land on one of the upper ledge blocks when you get there, just watch out for the Mightas lurking at the top.
The other way is to pop one of the Water Bubbles emerging from the bottom and let it carry you through to the top. The issue is, the water won't wrap back around to the top of the screen, leaving you vulnerable to the Mightas that are up there. Be careful if you take this route; bubble the Mightas as soon as you can, or immediately leap into the gate.
Remember not to kill the last enemy, or the gate will disappear! Leave it bubbled, and get to the gate. Also note, the gate will disappear immediately if the level enters Hurry Up.
If the unexpected happens and an Umbrella warps you past Round 20, don't despair! The Silver Gate will appear on the next level you play. The levels immediately after 20 are relatively easy, so this may be for the best.
Then, if you make it....
If all goes well and you made it to Round 20 without dying, then the special item for that stage will be the Silver Gate. Collect it, and you end up here.
There's a lot of weird things about this room, some of which are outside the scope of this article. (Try waiting for Hurry Up sometime and see what comes to get you instead of the Skel Monsta.) In game terms, you get 360,000 points in gems, you skip the next round, and you get a look at this mysterious mural in the background art:
It turns out these symbols are a code hiding a secret message for players who happen to get here. The key is in the top line, which is the 26 Latin/English letters, written out in what's called the Bubble Alphabet. It looks hard at first, but with practice it's possible to read messages written in it without great effort. Most of the letters are just flipped or rotated. See if you can figure out what this one says.
The information given here is not important, it's just telling you that, to win the game and get a "Happy End," you have to make sure to finish in two-player mode. But these screens have another purpose, to teach you how to read Bubblish. When you do win the game, there's another secret message for you, and it'll help a lot if you can already read it when it appears....
Bubble Bobble hides secrets even greater than this! Can you reach Round 100 and defeat the Super Drunk, and decode the message found after? I wish you the best of luck on your journey through the cave of monsters!
The best source of information on the game online is the excellent resource, The Bubble Bobble Info Page, by Stephen Tjasink and Paul Rahme. That page hosts a FAQ written by Chris Moore in 1998 that reveals the game's algorithm for generating special items.
BONUS: On SRPPs
Bubble Bobble is the most famous and most popular of the genre I've called "SRPPs," games where you're in a single room (usually just one screen in size), and, using your platforming skills, must clear all the enemies before heading to the next room. In the classic form of the genre, you have some distinctive means of attack for clearing out your opponents. These games very frequently have a large number of levels, usually 50 or more, and two-player co-op modes.
What isn't a SRPP? Joust and Balloon Fight aren't, because they're not platformers. The original Mario Bros may be an early example, but it's borderline because its levels all have the same layout. And Solomon's Key isn't about defeating the enemies.
What is a SRPP? These games, which are all originally arcade games unless otherwise noted:
Bubble Bobble's predecessor Chak'n Pop
Bubble Bobble, Bubble Bobble Part 2 (NES), and its direct sequels Bubble Memories and Bubble Symphony. Also, its storyline sequel Parasol Stars. Note however that its first arcade sequel, Rainbow Islands, is not an SRPP, because it's not about defeating all the enemies, and it scrolls up! And Parasol Stars, while an arcade-style game, never got an arcade release
Bubble Bobble's sibling games Fairyland Story and Don Doko Don, also made by Taito
Toaplan's Snow Bros, and its weird sequel Snow Bros 2 With New Elves
Mitchell's Pang, aka Buster Bros, and Funky Jet
Data East's Tumble Pop and Diet Go Go. Also Joe & Mac Returns (unlike the original Joe & Mac!)
Subsuno's Penguin Brothers
Irem's Yoyo's Puzzle Park for the PlayStation
Riot's Pop'n Magic for the PC Engine
NEC's Chip Chan Kick for the PC-FX
Kaneko's Wani Wani World for the Mega Drive (aka Genesis)
More recently, there's Cowboy Color's Handsome Mr. Frog for PC on Steam, and Whip! Whip! for PC on Steam, and Switch.
Thanks to brandon (@eryngi777), @zarawesome, and Misandrist Stache (@totesmcduck) for suggestions for this list. An old NeoGAF thread provided more suggestions.