If you want cored yoshis all you have to do is get to star road. One way i use is at the secret ghost house in world 2. First get the green palace. To get the green palace do the 2nd level in world 2. Where you get to the part with 3 bird swoopers and green dots go up the moving yellow ramp thing. You will see a green pipe. Go up the pipe. You will see that football player guy. Pass him. You will see yellow boxes going up like stairs but you have to jump. Any way go get the blue koopa shell to the right. Take the shell and aim up at the last box and a plant will come up the ones where you can climb ( i know i sound dumb but just for people who dont understand ;)) You will see a key and put it in the hole. Now complete the palace bla bla bla. Now go to the first level where you first get the feather. Go to the part of the level with the green dots. It's not dots anymore (duh) *slaps self* Go up and you'll see a key and hole yet again. Now do the secret level and do the ghost house. Now when you go the door pass the big boo keep going left pass the boo circle and get the p switch but dont activate it yet. NOw go back to the floating door but dont get in. Now by the door hit the boxes with a parana plant which you can climb and keep moving left too find a door. Now you fight big boo. To beat him use the blocks to kill him. When hes dead you'll be taken to star road. In star road you will find yoshi eggs. They will hatch. Feed the enemies to the yoshis until they grow into a normal yoshi. When you unlock them you can take them back in to the normal game or find them there like green yoshi. This is one way to get to star road. Here is an explanation on what the yoshis do.

blue yoshi: Everytime you eat a koopa shell you can fly
Red yoshi: Everytime you eat a koopa shell you spit out 3 fire balls
Yellow yoshi: Everyrime you eat a shell you can jump and make sand clouds and flip enemies

If you want to do these things without unlocking the yoshis you eat certain shells

blue shell: You can fly
Yellow shell: You can jump and make san clouds
Red shell: You spit out 3 fire balls
Green shells: You spit it back out and it can hit your enemies.


Thats all and a waste of my time but for the good of people so peace out.
I will show you how to get to star road in different ways if the ghost house is too hard.

Peace