Rainbow Islands

A sequel to Bubble Bobble. Following on from the end of that game, Bub and Bob have regained their human forms and now have to fight their way through the Rainbow Islands, seven differently themed islands each with different enemies and a huge boss at the end. Complicating this mission is the fact the islands are flooding, and each level must be completed before the water reaches the top, since the water kills instantly when touched.

The main difference between Rainbow Islands and its predecessor is the increased size of the levels, which are many screens high. It also introduces a new weapon for defeating bad guys; rainbows, which are fired in front of the player and have an arc shape, so that they can trap enemies, be stood or bounced on, and, most importantly, collapsed, which is the best way to destroy enemies.

The game has been praised for being surprisingly complex, largely due to its enormous array of potential collectibles and the various ways of obtaining them.

It has had a few Video Game Remakes:

Rainbow Islands Revolution (DS, PSP) (2005-08)
Rainbow Islands Evolution (PSP) (2007-08)
Rainbow Islands: Towering Adventure (Wii) (2009)

Tropes used in Rainbow Islands include:

Attack of the 50-Foot Whatever: Bosses.
Canon Discontinuity: The Bubble Bobble enemies have expanded versions of their attacks that never show up in later games.
Color-Coded Multiplayer: player 1 has to play as Bub (green shirt) and player 2 has to play as Bob (blue shirt).
Death Throws: In the US/Japanese NES version. Otherwise, the player character hits the platform he was shot off of.
Distressed People The player does not know this the first time around, though.
Everything Fades: An item that's been left alone disappears, with ambiguous but simple eight out-ward facing lines.
Everything's Better with Rainbows
Everything Trying to Kill You
Floating in A Bubble: In Rainbow Islands Revolution (DS), Bub is in a bubble and must be dragged around with the stylus. Japan is lucky to be able to use the D-pad.
Giant Spider: The first boss.
Gratuitous English / Blind Idiot Translation
Guide Dang It
Improbable Weapon User: Rainbows
Inexplicable Treasure Chests: A huge chest drops down at the end of each level.
It's a Wonderful Failure: If Bub/Bob gets trapped in the True Final Boss's bubble (thus getting re-transformed into a bubble dragon by it) on his last life, instead of a blank game over screen, he gets locked in The Alcatraz with eleven other victims who've also been transformed.
Kid Hero
King Mook: Some bosses are just huge versions of regular enemies.
Late Arrival Spoiler: It is a sequel to Bubble Bobble, so the characters are humans.
The Law of Conservation of Detail: No story details are shown until the player gets the first Bad Ending. Maybe those rainbow diamonds that disappear more quickly are important...
Multiple Endings
Not Quite Back to Normal: The One-Hit-Point Wonder factor still occurs even though Bub and Bob have turned back into humans.
One-Hit-Point Wonder
One-Winged Angel: The True Final Boss will reveal his true form after being defeated once.
Plot Coupon / Gotta Catch Them All : Big diamonds and mirrors.
Redheaded Hero
Remilitarized Zone: World 2. It's not called "Combat Island" for nothing.
Secret Level
Shout-Out / Nostalgia Level - so many that they take up a sizable chunk of the game! The entire fifth world, sound effects, enemies, boss and all, is a homage to Arkanoid, but the secret levels also are homages to Taito's other games. The last one, Bubble Island, is excusable, as this is the sequel to Bubble Bobble... still... Darius Island?
Stalked by the Bell: "Hurry!"
Super-Deformed
Super Drowning Skills - Bub or Bob die if they touch water.
Tertiary Sexual Characteristics: Three of the eleven Alcatraz victims in the final secret world are female green bubble dragons, each with a small pink bow on the corner of their head.
Theme Tune Cameo: The Bubble Bobble theme appears in this.
Theme Twin Naming: Bub(by) and Bob(by).
Toy Time: World 4.
Treasure Is Bigger in Fiction
Turns Red
Wingding Eyes: In an exaggerated variant, characters die with their eyes getting crossed off by a literal black line.