Taking place between the original Super Mario World 2: Yoshi's Island and DS, it turns out that the parents to which Mario and Luigi were delivered at the end of the former were not their actual parents. Surprised by the mistake, the Stork takes off to find the brothers' real parents, but gets attacked by Kamek once again, resulting in Luigi getting captured and Mario getting dropped, again. This time, Mario lands in the Yoshi's other home, Egg Island and the heroic Yoshis go off to reunite the to brothers and defeat Baby Bowser, who wants to turn Egg Island into his own personal resort.
New Island largely does away with the changes to gameplay introduced by Island DS, instead presenting itself as a more direct successor to the original Yoshi's Island. The art style itself is a mix of the original game's main art style with the claymation-style pre-rendered sprites from its intro.
This video-game provides examples of:
- Damn You, Muscle Memory!: Defied just like in DS, as there are two control schemes corresponding for the SNES and GBA versions.
- Eating the Enemy: Just like in previous games, Yoshi can eat enemies to turn them into weaponized eggs.
- Face Palm: The stork in the Yoshi's New Island intro upon realizing he brought Baby Mario and Baby Luigi to the wrong house.
- Fake Difficulty: The invisible clouds, which half of the game's red coins and smiley flowers are hidden in, which only appear (very transparently) for a split second at a time.
- Generation Xerox: While they've always looked more similar than different, Yoshi's New Island uses a design for Baby Bowser that is perfectly identical to Bowser Jr. in every physical detail, minus the bandana, retconning what few tiny physical differences there used to be and adding even more to frequent confusion between them. It also doesn't help that the voice they use are stock clips of Bowser Jr.'s voice that are raised in pitch.
- Giant Space Flea from Nowhere: Bowser appears this way. Unlike in DS, which had a story-based reason for his appearance, Bowser just shows up out of nowhere to be the True Final Boss.
- Happy Ending Override: It turns out that the Mario Bros. were delivered to the wrong house, leading to the events of Yoshi's New Island.
- Here We Go Again!: The opening cutscene for reveals the stork dropped Mario and Luigi off at the wrong house at the end of Yoshi's Island, and when he rushes to deliver the babies to their proper parents Kamek intercepts him and makes off with Luigi again.
- Identity Concealment Disposal: The epilogue in Yoshi's New Island reveals that Mr. Pipe, a warp pipe character that helps Yoshi if he loses too many lives in a incomplete level, is actually a time-traveling Adult Mario in disguise.
- Immediate Sequel: Yoshi's New Island begins right where the original game ends, making it an Interquel between it and DS.
- Interquel: Yoshi's New Island directly follows the original game, and thus is set before Yoshi's Island DS.
- Mercy Mode: If you fail a level three times, a character called Mr. Pipe gives you Flutter Wings that allow you to hover at a constant altitude. If you still fail a level even then, you receive the Golden Flutter Wings that make you invincible and allow you free flight.
- Nostalgia Level: The apparent final level, "Baby Bowser's Castle Break-In". Complete with Kamek ambushing, him suffering Bait-and-Switch Boss with Baby Bowser, Kamek then doing to the old Make My Monster Grow to him, them fleeing after his defeat, and the reunion of Yoshi, the babies, and the stork. And then adult Bowser ruins the whole thing.
- Sequel Difficulty Drop: The game is much easier than the original and especially DS. Indeed, some of the carryovers from the classic game have been simplified. Take the final boss fight, where the arena is much more forgiving, for starters, as you aren't threatened by bottomless pits.
- Sequel Reset: Yoshi's New Island actually starts with the original Yoshi's Island ending, revealing that the stork actually made a mistake and delivered the Mario Bros. to the wrong couple. So the stork is off to get the babies to the right parents when Kamek returns to capture them again.
- Theme-and-Variations Soundtrack: Yoshi's New Island features many (though not all) songs which are variations on the first level theme.
- True Final Boss: If you beat all levels without using the Flutter Wings, you will get to fight the adult Bowser.
- The Un-Reveal: The Mario Brothers' true parents finally appear in the epilogue of Yoshi's New Island. Like the couple in the prologue, though, they are silhouetted and their faces aren't shown, leaving their identities up to our imagination.