How to Find Yoshi in Super Mario 64

Make sure that you have gotten all 120 stars that are in the game and that you have beaten the third Bowser.

Go outside in the grass of the Castle Grounds. Once you are there, from Peach's castle, head down and straight ahead to the area that has yellow ground as well as water.

Notice the cannon that is over there. You probably may have noticed that you may have seen while playing outside the Castle Grounds, but couldn't use (because it had a grating over it's opening) will now already be in use. earlier in the game, because you haven't gotten all of the stars. If you currently have all 120, the grate over the top should be gone and the cannon should now be open.

Get into the cannon.

Aim for the roof. Don't aim for the very top. But instead aim at the little flat bit at the sides of the huge spire at the top of castle. Remember, Mario does not have a straight trajectory and is a fast faller, so be sure that you aim the cannon a little bit higher, as if he slides or falls off of the castle, he will either lose a lot of health or die.

Press the a button on your controller once you're aimed to shoot Mario out of the cannon.

Know that if you managed to get to the top of the roof, you will meet Yoshi. He will give you a special message from Shigeru Miyamoto, Mario's creator, to you, the player, give you an extra hundred lives, and he'll make your triple jump sparkly.