Yoshi's Island is unlocked from the start. It is also Yoshi's home stage.
This stage has a unique design. On the far right of the stage, there is a hill sloping downwards. You can do up the hill, but if you walk too far it could result in a side screen death. You are also closer to the top of the screen death area, so don't go up to far. On the left side of the screen, there is also a little hill that slopes upwards, but at the end of it is a warp pipe (which you can't go down in.) In the center of the stage is 9 yellow blocks. Six of the blocks are in the air, while three of them are in the middle. Below the three middle blocks is a pit. If you hit a block, they will start spinning. You won't be able to stand on the blocks while you they are spiining. Be careful when fighting near the 3 center blocks as it is easy to fall down into the pit and you will most likely die.