Welcome To Yoshi's Island is a level that can be played only once when a new game is started in Super Mario World 2: Yoshi's Island and its remake, Yoshi's Island: Super Mario Advance 3. It is mainly a tutorial in which Yoshi learns about Baby Mario, as well as using an Expansion Block and collecting coins. The level is very basic and short with no collectibles, with only a few Shy-Guy enemies strolling around, making it easy enough for beginners. In Super Mario World 2: Yoshi's Island for the Super Nintendo Entertainment System, the level does not feature the Extra life system, and thus, the player cannot get a Game Over; in Yoshi's Island: Super Mario Advance 3, if the player gets a Game Over in this level and chooses to stop playing, the file will say that the level is World 0. This level is also called World 0 if the player pauses during the level in Yoshi's Island: Super Mario Advance 3; it says "World 0" at the top, and at the bottom, it says the level is "World 0-0." As the level ends, Yoshi begins level 1-1, Make Eggs, Throw Eggs.
The level is also used as the final section of Endless World of Yoshis, with the addition of Kamek attacking Yoshi every few seconds as in the first section of King Bowser's Castle.
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(without turning the game off) and starts a new file, the color of the Yoshi played as in this first level will be the color of the Yoshi Baby Mario was passed to instead of Green Yoshi.