Bubble Bobble/Secret rooms

If a player can survive until stage 20, 30 and 40 without losing a life, a door icon appears. If you reach it before it disappears, it 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.

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 room 20

 * Secret Message: If you want to become the old figure, use the power of your friendship, and fight with me!
 * Explanation: The message explains that the players must reach Super Drunk (depicted in the statue of the center of the room) to become human. The tone of the message suggests that the messages are written by Super Drunk himself.

Secret room 30

 * Secret Message: I enclose these magical medicine here, because those are my worst fears....
 * Explanation: Super Drunk 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.

Secret room 40

 * Secret Message: 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 Super Drunk together. It is impossible to see the true ending of Bubble Bobble in single-player mode, unless a second player joins in during the Super Drunk battle.  "Love of truth" is evidently an erroneous form of "true love".

Rascal
Dying inside of a secret room is possible, if killed by the secret room's time up monster, 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.

Additionally, losing your last life in a secret room will trigger a glitch in the next new game, causing the player to be transported automatically from round 1 to the secret room where the last life was lost in the previous game. 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.