CAVE of MONSTERS

The Mechanical Prototype Bubblen (ばぶるんろぼ Baburun Robo, "Bubblun Robo"), serial number Code No. CR20 - 100190 is a sub-boss character that appears at the end of Bust-A-Move 2's Player VS Computer Story Mode. It is a giant robot created by Dreg in order to disguise himself as Bub. It is the only character in the history of the PUZZLE BOBBLE series to use it's own canon to shoot the bubbles instead of the regular arrow. Defeating the robot will reveal it is being controlled by Dreg from its cockpit.

It is introduced as a HUGE BATTLESHIP with a warning when Bub first meets it, a callback to a previous TAITO game, Darius. Upon meeting the robot, Bub appears to be terrified of it. The robot never made any more appearances in any other Puzzle Bobble games, however it does appear in Pop n' Pop, being Dreg's mode of transport to the levels he is active in, exiting through the cockpit before the battles begin.

The Prototype Bub returns in Pop'n Pop as Dreg's method of transportation and brings him to the match before the battle takes place.

While it does not serve any other purpose, at least it confirms that it is still in service and functional after the events of Puzzle Bobble 2. It's worth noting that Prototype Bub is not being used as a weapon in Pop'n Pop as Dreg clearly exits it before the battle begins, unlike in Puzzle Bobble 2 in which it is used in a threatening manner (most probably because in that game, it is defending Dreg's Castle from Bub.)

• Puzzle Bobble 2/Bust-A-Move 2
• Pop n' Pop

Prototype Bub has its own unique bubble machine. Instead of an arrow, it uses a metal cannon. It seems to be very adept at using this, though it is generally harder for others to aim with it. Prototype Bub also has a unique condition that allows it to be on the top layer. This means that bubbles that descend down the screen become covered up by its huge frame, making it impossible to see what colours they are. This does not affect it in the story as it is computer controlled, but by the use of Character Building Cheats, playing as Prototype Bub becomes considerably difficult.

Due to it's huge size and the character select for Puzzle Bobble 2 being a "secret/cheat", bubbles that drop too low become hidden behind the P.Bub. This was most likely an oversight by the game developers at the time since it was never really intended for the player to be able to select it as a character by any conventional means, and the computer controlled characters do not need the bubbles to be visible in order to detect them. Later games in the series corrected this for large characters by making the bubbles the top layer.