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[edit] Levels

Each level (or round) consists of one screen, with no scrolling or flipping. The dragons can move around the levels by walking on platforms, falling through empty space, jumping through platforms from below and (in some levels) falling through holes at the bottom of the level in order to reappear at the top, or even vice versa (see gameplay techniques below).

Apart from jumping, the characters can blow bubbles. Bubbles also float in from the top or bottom of the screen in many levels. They pop after a certain amount of time, when they hit the dragon's spiked back, if they're squashed against a wall or another dragon or if they're fallen upon. By holding down the jump button, it's possible to bounce on top of bubbles, which is sometimes necessary to reach platforms. The main objective of the game is to trap enemies in bubbles, and burst them, destroying the enemies. Defeating several monsters at once awards exponentially increasing point awards.

Each round also features invisible air currents and custom bubble physics, causing bubbles to move in predetermined trajectories, such as converging to a certain point, moving very quickly or very slowly, being pulled down as if by gravity, etc., usually with notable effects on a level's difficulty.

Some levels have very short bubble-popping times, meaning that bubbles pop almost as soon as they emerge. This becomes extreme in later levels to the point of only being able to kill monsters by "kissing" them (blowing a bubble in such a way that it's immediately squashed against the dragon, causing instant death to an enemy). Time limits are also used to increase the game's difficulty; two rounds having no time limit, some levels are almost impossible to finish under certain conditions (single player, lack of certain bonuses etc.). When the time limit expires, the player does not die instantly, but rather an invincible "Skel" (see below) enemy appears for each player, and all enemies become 'angry', with a change in color and increase in speed.

[edit] Secret rooms

If a player can survive until stage 20, 30 and 40 without losing a life, a door icon appears that, if collected in time, transports Bub and/or Bob to one of three secret rooms. Along with 36 diamonds, there is a coded message written on a plaque at the bottom of each room. The first line of this indicates the alphabet and the text that follows is a cryptic message explaining various game tips.

Transliterating the messages, they read as (spelling and grammar as they appear in the game):

First Secret room (with a Grumple Gromit statue (with his eyes struck out)): "If you want to become the old figure, use the power of your friendship, and fight with me!".

Explanation: The message essentially tells the players that they have to reach Grumple Grommit to become human. Also, the tone of the message suggests that the messages are written by Grumple Gromit himself.

Second Secret room (with a big broken Lightning bottle): "I enclose these magical medicine here, because those are my worst fears....".

Explanation: Grumple Gromit explains his weakness to thunderbolts, which is indeed the weapon that players must use against him; the final level provides the Lightning bottle, which enables the players to breathe lightning bubbles.

Third Secret room (with a heart under a glass pane): "If you want to get back your love of truth you must help each other until the last....".

Explanation: Perhaps the most cryptic of the three messages, this refers to the fact that the game cannot be truly "won" unless both players reach the final round and destroy Grumple Gromit together. (It is thus impossible to see the true ending of Bubble Bobble in single-player mode, unless a second player joins in during the Grumple Gromit battle.)

This coded alphabet is used to display the "Super Mode" code (after finishing the game with two players in 'standard' mode), and appears in several other Taito games, like Rainbow Islands and the Puzzle Bobble series.

Secret doors appear on levels 20, 30 and 40, with one that skips you forward 20 levels if you make it to stage 50 without dying. [1]

Dying inside of a secret room is possible, if killed by the secret room's time up monster, called Rascal. If that happens, the player will lose a life and if that was the player's last life, the game will end by causing the maximum reached round to be "Round 102" for the first secret room, and "Round 103", "Round 104" for the second and third, accordingly.

Performing the previous actions will also trigger a glitch in the first new game started, by causing the player to be transported automatically from round 1 to the first (or second, or third, depending on where the last life was lost in the previous game) secret room. This will also disrupt the order in which secret rounds appear, by making them appear earlier. In the second secret room, the thunderbolts actually seek out the players themselves, and by parking a player to the far right side of the round, will cause the thunderbolts to start striking on the far left side and eventually re-emerging from the right side.