Rainbow Islands Evolution

Rainbow Islands Evolution is a game in the Bubble Bobble series for the PSP system.
Bub and Bob, the two main characters in the series, are against an evil recording company that seeks to pollute the Rainbow Islands' atmosphere by creating constant musical noise, therefore wilting the flora and mutating the fauna. In this game, Bub and Bob use a weapon call the "hurdy-gurdy" to create the rainbows.
The game follows the same vertical-scrolling system from the original, but it expands to a third dimension as there are platforms in the background which become accessible through the course of the game.

Source: Wikipedia, "Rainbow Islands Evolution", available under the CC-BY-SA License.