Bubble Bobble/Gameplay

Game mechanics
The original arcade game, despite its 1986 release date and its apparent simplicity, features some rather complicated and convoluted game mechanics, one of the main reasons that many computer or game console ports of the game, even when released several years after the original, can seem lacking and incomplete in some aspects.

Weapon
The dragons' main weapon is their ability to blow bubbles. After being blown, they shoot forward for a short distance, then start to float upwards or along a wind current. It is possible to jump on bubbles to reach otherwise inaccessible areas. An enemy hit by a forward-shooting (not floating) bubble will be trapped in it. The bubble can then be popped, killing the enemy and turning it into an item that can be collected for bonus points. If left floating, it will become angry and escape the bubble after a while.

Items can be collected to increase the firing rate or range of the bubble, or replace the bubble attack with a different one.

Playing techniques and styles
Bubble Bobble is a game heavily relying on gameplay and precise technique rather than graphics, and it features a series of special techniques and tricks a player can perform to maximize his or her score, make some rounds of the game easier or faster to finish or just to be able to survive or even finish a round.

Some of these techniques have special nicknames, which may differ from player to player and from country to country.


 * Kissing monsters or just kissing means killing a monster by blowing a bubble at almost contact distance: the monster will be instantly bubbled and the bubble will be instantly popped, giving the visual effect of the player killing a monster with a "kiss". Some players flip their joysticks in the opposite direction after pressing the bubble buttons, giving more chances of an "instant pop" and changing flight direction for the dead monster. This technique is useful in stages where monsters move too fast, bubbles last for too short a time or it's otherwise hard to bubble them normally. Of course good timing is required for this technique to work.
 * Riding bubbles means keeping the jump button pressed when dropping on a bubble: if done correctly, instead of popping the bubble, your dragon will instead jump on it, possibly continuously, enabling him to "ride" bubbles in order to reach otherwise unreachable areas. Some stages can't be finished without this technique.
 * Climbing is a step up from riding bubbles. It means standing at half a bubble distance from a wall, jumping and blowing a bubble almost simultaneously, jumping up from that bubble and blowing another bubble and so on. This is necessary if the air current pushes down bubbles but you need to climb up. Having the rapid-bubbling power-up (the yellow candy) makes climbing a lot easier, especially if you got the running shoes already.
 * Bubbling oneself through means "riding a bubble" through the opening at the top of a stage or even just through the ceiling of a stage in order to appear at the lower part, like some flying monsters can do. This technique is required to finish some stages or to get unstuck from some places, or just to save time.
 * Blowing against the wall means blowing bubbles against wall at contact distance: the bubbles will pop immediately thus giving the player 10 points per bubble pop. This can be used to either increase a player's score, or to set a player's score to a specific amount, in order to do other tricks.
 * Two equal digits means using the "blowing against the wall" technique or other score-adjusting techniques in order to make the two penultimate (100s and 10s places) digits of at least one player equal, e.g., 456770, before the last enemy bubble is burst. If done correctly and the score is not modified when this occurs, then all remaining non-special bubbles on screen will be turned to 700-point bonuses, whose appearance depends on the digit picked. E.g., 7 gives Chocolate Ice Creams, 3 gives Hamburgers, and so on.
 * This trick is easier to do with two players (one player adjusts his score and the other bursts the bubbles), but it can also be done with only one player, although calculating exactly how much (and if) one's score will be modified when bursting the last enemy bubbles can be extremely complex, if not unpredictable, especially if there are very large and clustered bubble bunches.
 * Rounds with numbers ending with 5 and 0 up to and including level 50 generate bonuses from bubbles automatically, though, and some rounds (including round 1) do it by default.

E-X-T-E-N-D
A relatively unknown and obscure part of Bubble Bobble gameplay has always been the way the various bonuses appear. While most of them may appear completely random, the game actually keeps a series of internal (and unseen) counters about events such as number of jumps, jumps over bubbles, bubble bursts, bubbles blown etc. during a round or in the whole game, maximum number of monsters blown in a certain round etc. and these events are actually used to determine which bonuses will appear, and to a certain extent when they will appear.

Some known events and the effect they have on bonuses are:

The number of distinct EXTEND bubbles that will appear on a round depend on the maximum number of monsters killed during the round, or on a previous round if said previous round didn't have "openings" for EXTEND bubbles to fly in, or was completed before they could appear. In general, killing N+2 monsters will make N distinct EXTEND bubbles appear. Since the game actually can have only 7 monsters per round, killing 7 monsters in a single bubble cluster will make 5 EXTEND letters appear.

In Taito's PC port, however, killing N monsters will cause the N-th letter of the word to appear - making the N extremely hard to get because there's only few levels where you can easily pop five enemies simultaneously. This is probably a bug.

Another known event-triggered event is the appearance of candy cane bonuses: if a player rides a bubble more than 20 times, then a candy cane will surely appear in that round.

Other bonuses can be made to appear in similar manners, and there is at least one internet page listing some of the events and their effects.

For a special bonus on the NES version, a player must enter the password HIJID, select 2 player continue, and finish round FO (last level) with both players alive. After the entire ending has run and the player is prompted to press start, the player will receive a reward. The reward is a sound test for the whole game.

Continues
Bubble Bobble allows continues to be used when a player runs out of lives. While most arcade games display a continue timer before returning to the title screen, Bubble Bobble ends immediately once there are no players in the game.

A single player can cover for the other player returning to the game. However, a lack of second player requires a credit within the machine, as well as holding down the start button just before the game ends.